The Glasgow charity for nackered seafarers have suffered a fire onboard a vessel and the dc generator onboard the vessel have been severely damaged and categorized as unfixable. As a suitable replacement for the generator is not available in the market and it is quite expensive to build a new generator, we have decided to retrofit the existing DC generator with an AC alternator. It should also be taken into account that only the electrical side is damaged the engine is still functional.
OBJECTIVE:
Primarily the main objective of this project is as stated above is to "retrofit the DC generator with an AC alternator". Secondly we will provide the same power which is 500 KW at 500 RPM , and we will use a bridge rectifier which will convert the AC supply into DC and in between them we will put a Air circuit breaker which will protect the rectifier and all other equipments from damage due to high current or over load current and from short circuit.
The Basic Concept:
The operation of Alternators is based on the principle of that each time there is joint cutting flanked by a conductor and a magnetic field, a voltage and a consequential current will be induced in the conductor.
The induced electromotive force (emf) flow is not an unsystematic but Fleming's Right Hand rule defines that it as the direction of motion of conductors with reverence to the magnetic field.
Conductor motion
South pole / Magnetic field / North pole
Alternator:
For prime movers the basic sources of fuels are as follows:
Fossil Fuels engines driven by diesel, petrol, kerosene etc.
Conventional prime movers for example gas, steam and water turbines.
Non-conventional engines for example wind, wave, tidal energies.
Futuristic - Nuclear, Solar and Biomass Energy.
The sequence used for the alternators to take advantage of or exploit the principle of generation the revolving poles of the magnetic fields which moves in the permanent conductor and produce joint cutting flanked by the conductor and magnetic fields.
The rotor has a pair of poles so that the output is generated simultaneously in two conductors. By referring to the
Fleming's Right Hand Rule it will be confirm that the direct direction of predictable current indicated by the arrows. The two conductors are linked in series so that the voltages generated in them are added jointly to deliver current to the switchboard. The rotating fields although moving at stable speed which will cut the conductors at a varying rate because of the circular movement. The Voltage induced at any instant is proportional to the sine of the angle of the rotating vector. The pattern of build-up and decline and also a reversal in the voltage induced is shown by the sine wave.
The Voltage and the current are generated in each pair of conductors in turns, first in one direction and then in the other direction to produce three-phase alternating current. The effect in conductors Y and B is also shown in figure.
A Simple Alternator & its Sinusoidal Output (Wave-form)
Stator Construction:
The stator is a tube made up of silicon iron laminations with axial slots along the inside surface in which the conductors are laid. The importance of the iron stator is based in its ability to strengthen the rotor magnetic fields, which cut the conductors.
Ventilation ducts
The iron stator is also a conductor and will have like the conductor's voltage and current induced in it by the rotating fields. It is to prevent circulation of unwelcome eddy currents that the stator is made up as a laminated structure of steel stampings.
Rotor Details:
An alternator rotor has one or more pairs of magnetic poles. Residual magnetism in the iron core is boosted by flux from direct current in the windings around them and this current from the excitation system has to be adjusted to maintain constant output voltage through load changes.
With the exception of brushless alternators, the direct excitation current for the rotor is supplied through Brushes and slip rings on the shaft. The copper-nickel alloy rings must be insulated from each other and from the shaft. They are shrunk on to a mica-insulated hub (which includes in class H insulation), which is keyed to the shaft. Brushes are of an appropriate graphite material and pressure is applied to them by springs.
Cylindrical Rotor Construction:
The cylindrical rotor is constructed with axial slots to carry the winding, which forms a solenoid although not of the usual shape. Direct current from the excitation system produces a magnetic field in the winding and the rotor so that N - S poles are formed on the areas without slots.
A Cylindrical or Turbo Alternator
One rotation of the single pair of poles will induce one cycle of output in the stator windings (Conductors).An alternator with one pair of poles has to rotate at 50 times per second to develop a frequency of 50 cycles per second. In terms of revolutions per minute, the alternator speed must be
60 x 50 = 3000 r.p.m. (f = PN/,,O).
Salient field poles are those which are secured to the periphery of the alternator rotor and therefore project outwards. The word 'salient' describes only the physical construction of the rotor; it is not an electrical term.
Low Speed Alternators:
The Alternators which are designed for rotation at lower speeds with slower prime movers have a greater number of pairs of poles (as shown in diagram). One pair of poles induces only one complete cycle in the stator windings per revolution, and where for our requirement, an engine-driven alternator is intended for operation at 500 r.p.m., it requires six pairs of poles or we can say that 12 poles. The number of pairs of poles, P. is found from the proposed speed and system frequency.
P = 120F/ N.
Rotor diameter is larger on slow-speed machines in order to accommodate the large number of poles, but low rotational speed produces less stress from centrifugal force. The flywheel effect is beneficial and this together with careful balance and improves smooth running.
End Rings
(Relation between the number of poles and the revolutions per minute at 50 Hz frequency).
Poles
RPM at 50 Hz
2
3,000
4
1,500
6
1,000
8
750
10
600
12
500
14
428.6
16
375
18
333.3
20
300
The output frequency of an alternator depends on the number of poles and the rotational speed. The speed corresponding to a particular frequency is called the synchronous speed for that frequency's.
Difference Between Insulations:
In this Alternator we will use class A insulation and the difference between class A insulation and other insulations for example (class H, class B, class E and class F insulation) is give below, it will explain that why we have used class A insulation and how it is more effective than other insulations. However mostly marine ships use class A insulation.
Class A Insulation:
These are the materials or combinations of materials such as cotton, silk, and paper when correctly impregnated" or covered or when absorbed in a dielectric liquid such as oil. Other materials or combinations of materials might be integrated in this class if experience or accepted tests can expose their capability to operate at 105degree F to 211 degree F).
ADVANTAGES:
A majority of marine equipment has been insulated with Class A materials and to a lesser extent with Class B, but Class E is also becoming popular. Here, full advantage is being taken of the synthetics in enamels and similar materials now in use, which are suitable for higher working temperatures. These are better than the oleoresin enamels which were available when the limits for Class A materials were established.
An insulating material is considered to be 'suitably impregnated' when a suitable substance such as varnish penetrates the interstices between fibres, films, etc., to a degree adequately to bond components of the insulation structure and to provide a surface film which adequately excludes moisture, dirt and other contaminants.
For some substances, compounds and resins without solvents may be used which substantially replace all the air in the interstices. In other applications, varnishes or other materials containing solvents may be used which provide reasonably continuous surface films and partial filling of the interstices with some degree of bonding between components of the insulation structure.
The insulating material is said to be 'suitably coated' when it is covered with a suitable substance such as varnish which adequately excludes moisture, dirt and other contaminants to a degree sufficient to provide adequate performance in service.
Class B Insulation:
These are the materials or combination of materials such as mica, glass, fibre, etc, with appropriate bonding substances. Other materials or combination of materials not necessarily inorganic they may be included in this class if accepted tests can disclose their capability to operate at (130 degree F to 266 degree F).
Class E Insulation:
These are the materials or combination of materials which experience a test that can reveal their capability to operate at 120 degree F to 248 degree F) (Materials possessing a degree of thermal stability allowing them to he operated at a temperature (15 to 17 degree F than Class A material).
Class F Insulation:
These are the materials or combination of materials such as mica, glass, fibre, etc, with suitable bonding substances. Other materials or combination of materials, not necessarily inorganic, may be included in this class if, experience or accepted tests can show them shown to be capable of operation at (115degree F to 311 degree F).
Class H Insulation:
These are materials or combinations of materials such as silicone, elastomeric, mica, glass, fibre, etc, with suitable bonding substances such as appropriate silicone resins. Other materials or combination of materials, not necessarily inorganic, may be included in this class if, experience or accepted tests can reveal their capability to operate at 1 80 degree F to 356 degree F).
ALTERNATOR:
The alternator which we are using is classified as below;
Specification:
Rated speed of an alternator 500 (R.P.M)
Rated power of an alternator 500 (KW)
Rated frequency of an alternator 50 (Hz)
Poles of an alternator 12 (Poles)
Power factor of an alternator 0.8
Insulation Class A
Rated voltage 440volts
Calculations:
For line current of an alternator:
This we are finding because with the help of this we will calculate the line current.
Formula
Power = √3Ã-line voltage line Ã- line current Ã- power factor
Since
Power = 500KW
Voltage line= 440 v
Power factor= 0.8
Line current=?
Now,
Line current= power /√3 Ã- line voltage Ã- power factor
So,
Line current= 500000/√3 Ã- 440 Ã- 0.8
Therefore,
Line current= 821 amp
CALCULATION FOR PEAK LOSS:
With this calculation we will find the peak loss means the voltage loss which occurs at the peak of the wave form.
Vdc= 2Vp/Î
Where,
Vdc= 220 V
Î = 3.142
Therefore,
Vp= 220/2*3.142
Vp=345v
Peak loss =345-220= 125v
After calculation the output dc voltage is 220 V
So there is a peak loss of 125v
Now we are calculating the input AC voltage for the rectifier after then we will obtain the 220 DC voltage.
Data:
Vp = 440v
Vs = ?
Np = 5
Ns = 6
Solution:
Formula used:
Vp/Vs = Ns/Np
Vs = Vp*Np/Ns
Vs = 440*5/6
Vs = 366.66volts.
Now we are calculating the over current relay (OCR) for circuit breaker for its protection from short circuit and other damages.
The full load current is 821 amps, so the alternator current relay will trip at 125% Ã-821=1026 amps.
Excitation System:
The excitation system is consisting of both supply and control the direct current for the rotor's pole windings in the case of a rotating field stationary armature alternator. The level of the excitation current and resulting pole field strength is automatically adjusted by the voltage component known as Automatic voltage Regulator (AVR).
Vibrating Contact Regulator:
The operating coil of a vibrating contact regulator is similar to that of the carbon pile type. It is supplied with a transformed and rectified current from the alternator output and the field of the Electromagnet is used to attract an iron armature against a spring. The spring acts as a voltage reference and the strength of the electromagnet is related to the alternator's output voltage. Increase of output voltage produces an increase in strength of the magnet, and the effect is that the plunger and lever are pulled up together with the control contact. A drop in voltage and decrease in strength of the coil allows the plunger to be pulled downwards by the spring so that the control contact also moves down. The alternator voltage governs the position of the control contact across the coil.
Conventional Alternator and DC Exciter with Vibrating Contact AVR
Transient Voltage Dip and Alternator Response:
A gradual change of alternator load over the range from no load to full load would allow the automatic voltage regulator (AVR) and excitation systems described, to maintain terminal voltage to within perhaps 2% of the nominal figure. The imposition of load however is not gradual, particularly when starting large direct on-line squirrel cage induction motors. Starting current for these may be six times the normal value and their power factor is very low, at say 0.40 while starting.
CABLES:
The cables which we are using are classified below; in this specification it is shown that the current rating is 918 Amps, it is for each cable and there we have used three cables for three phases although our line current or full load current for each phase is 821 Amps which is shown in calculation. The Amps rating in cables is higher because it is safer as our requirement is 821 amps but we are using 918 amps actually it is the capability of the cable to stand with. We have used copper cables instead of Aluminium because it is thinner than the aluminium and it can be fit in to duct spaces. It can be easily jointed and they can carry high current without rising the ambient temperature above 90 degree. Copper is a good conductor of electricity hence it is more efficient or provides more efficiency than Aluminium.
SPECIFICATION:
Conductors----------------------------Tinned annealed stranded copper
Insulation------------------------------MGT (Mica Glass Tape) with EPR (Ethylene Propylene Rubber), white insulation with black numbers
Sheath/Jacket---------------------- Low Smoke Zero Halogen (ZHAL), type: SW4
Colour--------------------------------Black
Voltage-------------------------------440 volts
No of cables--------------------------3 cables
Current in each cable---------------918 amps
Conductor cross sectional area-------------------500 mm2
Voltage drop ---------------------------------------- 0.29 A/m.
Operating temperature of conductor-----------Maximum 90 degree
Standards--------------------------- BS6883: shipboard cable, BS7917: fire resistant shipboard cable.
CIRCUIT BREAKER:
The circuit breaker is a device which is used to open or close an electrical circuit for normal and abnormal operation condition. The circuit breakers are made for work to energize and de-energize loads. When the current becomes very high the circuit breaker opens to prevent all possible damages to equipment and surroundings due to high current. The short circuit is usually caused by the excessive currents, and these are created by lightening, accidents and continuous over loads.
AIR CIRCUIT BREAKER:
In air circuit breakers, the air is compressed up to the high pressures. A ballast valve opened to release the high pressure air in to the ambient when the parts in contact, this will create a very high velocity flow close to the arc to disperse the energy. In sulphur hexafluoride (SF6) circuit breakers the same operation or method is applied in which sulphur hexafluoride is used as the medium at the place of air. In the "puffer" type SF6 circuit breakers the motion of the contacts is compressed by the gas and forces it to flow through an orifice beside the arc. These both types of sulphur hexafluoride circuit breakers are introduced for extra high voltage transmission by the system.
Short-circuit current:
The circuit breakers are manufactured to carry normal expected currents and when there is short circuit current they can be safely interrupt or discontinue.
The current will be very high under the short circuit condition, when the electric contacts are open to discontinue a large current and there is a tendency for an arc to from among the opened contacts which would allow the current to continue.
The condition creates conductive ionized gases and vaporized metal which cause further continuous flow of an arc or the addition of short circuit can be created which consequences in the explosion or destroy the circuit breaker and the equipments which are to be installed for use, therefore the circuit breaker must include different features to divide and differentiate the arc.
Types of circuit breaker
Front panel of a 1250 A air circuit breaker manufactured by ABB. This low voltage power circuit breaker can be withdrawn from its housing for servicing. Trip characteristics are configurable via DIP switches on the front panel (A).
There are different classifications of the circuit breaker which can be based or made on the features of such as voltage class, manufacture type, disturbance type and structural descriptions.
Low voltage circuit breakers:
The low voltage circuit breakers are less than 1000 VAC. These types of circuit breaker are commonly used in domestic, commercial and industrial applications and it includes;
Miniature circuit breaker (MCB).
Moulded case circuit breaker (MCCB).
We have selected an Air circuit breaker which works at low voltage and we have installed it in between new alternator and new rectifier.
The difference between miniature circuit breaker and moulded case circuit breaker is defined below;
Miniature circuit breaker:
In miniature circuit breaker the current rating is not more than 100A and the trip characteristics are normally not adjustable, they can perform thermal or thermal-magnetic operations.
Moulded case circuit breaker:
In moulded case circuit breaker the rating of current is up to 2500A and they can also perform thermal and thermal-magnetic operation and the trip currents can be adjustable.
So that we will adjust the tripping current 125% above the full load current which are 821 Amps and the required calculations are already done.
The low voltages circuit breakers can be installed in multi tier low voltage switch boards or switch gear cabinets.
The low voltage circuit breakers are characterised by an international standard as IEC 947. The purpose of these circuit breakers is normally installed in sketch out enclosures which allows elimination and interchanges without disassembly the switch gear.
The large low voltage circuit breakers have an electrical motor operator, which allow then to be tripped (opened) and (closed) under the remote control action. These can be installed in an automatic transformer switch system for standby power.
The low voltage circuit breakers are also prepared for the direct current (DC) applications. Especially the circuit breakers are build for direct current supply (DC) in which the arc has not a accepted inclination to go out on each half cycle as it goes for an alternating current. The Direct current circuit breakers have blow out coils which creates or generator magnetic field the rapidly stretches the arc when discontinuing the direct current.
®The circuit breaker which we will use in this system is classified as below;
Specification of Circuit Breaker:
Frame size------------------------------------------------AR2
Performance type---------------------------------------S
Rated current---------------------------------------------1205 amps
Model-------------------------------------------------------AR 2125
Service breaking capacity, (Ics) KA 440V AC----------65
Short circuit with stand-----------------------------------1 second
Mechanical Endurance ------------------------------------30000
(Operating cycle) with maintenance.
Thermal operation
Electrical Endurance (operating cycle) 460V AC-----12000
Adjustable LSI
Adjustable Ground fault
Adjustable Indication contacts
Alternator & System Protection:
Introduction;
Protective devices are built into main alternator breakers to safeguard both the individual alternator and the distribution system against certain faults. Over current protection is by relays which cut power Supplies to non-essential services on a preferential basis, as well as breaker overload current trips and instantaneous short-circuit current tripping. A reverse power trip is fitted where alternators are intended for parallel operation (in some vessels they are not), unless equivalent protection is provided by other means. Parallel operation of alternators also requires an under-voltage release for the breaker.
Over-current Protection:
Various methods are used to detect over-currents in a circuit. They have an inverse current-time characteristic, i.e. the higher the current, the faster will it operate. A few of these are:
Magnetic
The solenoid drives an iron core to operate a 'trip' switch. The core movement is 'slugged' by either an oil dashpot or a mechanical delay (clockwork action).
Thermal
A thermal relay utilizes the bending action (or rather the coefficient of expansion) of a bimetallic bar to trip the circuit breaker. The time taken to heat the bimetal gives the necessary time lag.
Electronic
An electronic over current relay usually converts the current into a proportional voltage. This is then compared with a set voltage level within the transistorized monitoring unit. The time delay is obtained by the time taken to charge a capacitor. This type of relay usually has separate adjustments for current trip level and for trip time. The amplifiers within' the electronic relay require a power supply (usually 110,220 or 440V a.c.).
Both the magnetic and electronic relays can be set to give an almost instantaneous trip (typically 0.05 sec.) to clear a short-circuit fault. Thermal relays are commonly fitted in moulded case circuit breakers (MCCBs) and in miniature circuit breakers (MCBs) for overload protection.
So we will use Thermal protection because it is suitable for the circuit breaker which is to be used.
The alternator breaker has an over current trip, but a major consideration is that the supply of power to the switchboard must be maintained if possible. The breaker is therefore, arranged to the tripped instantly only in the event of high over current such as that associated by the short circuit. When over current is not so high, a delay with an inverse time characteristic allows an interval before the breaker is opened. During this time the overload fault may be cleared.
Overload of an alternator may be due to an increased switchboard load or due to a serious fault, causing high current flow. Straightforward overload (apart from the brief overload due to the starting currents of motors) is reduced by the preference trips which are designed to shed non-essential switchboard load.
Preference trips are to be operated by relays set at about 125% of the normal full load. They open the breakers feeding ventilation fans, air conditioning equipment. The non-essential systems are disconnected at timed intervals, hence reducing alternator load. A serious fault on the distribution side of the switchboard should cause the appropriate supply breaker to open, or fuse to operate, due to over current. Disconnection of faulty equipment will reduce alternator overload.
Reverse Power Protection:
Alternators intended for parallel operation are required to have a protective device, which will release the breaker and prevent motoring if a reversal of power occurs. Such a device would prevent damage to a prime mover, which has shut down automatically due to a fault such as loss of oil pressure. Reversal of current flow cannot be detected with an alternating supply but power reversal can, and protection is provided by a reverse power relay, unless an acceptable alternative protective device is fitted. The reverse power relay is similar in construction to an energy meter as shown in Figure. The lightweight non-magnetic aluminium disc, mounted on a spindle, which has low-friction bearings, is positioned in a gap between two electromagnets in which the upper electromagnet has a voltage coil known as (primary coil) connected to the transformer in between one phase and an artificial neutral of the alternator output where as the lower electromagnet has a current coil which is also known as (secondary coil) is also supplied through the same phase by the transformer.
The voltage coil is designed to have high inductance so that the current in the coil lags the voltage by an angle approaching 90'. Magnetic field produced by the current similarly lags the voltage and also lags the magnetic field of the lower electromagnet. Both fields pass through the aluminium disc and cause eddy currents.
The effect of the eddy currents results in a torque being produced in the disc by the normal power flow and the trip contacts which are on the disc spindle are open and bears against the stop. When power reverses, the disc rotates in the other direction, away from the stop, and the contacts are closed so that the breaker trip circuit is energised. A time delay of 5 seconds prevents reverse power tripping due to surges whilst synchronising. Reverse power settings are 8% to 15% diesel engines prime movers.
Under-voltage Protection:
Conclusion by error of an alternator breaker when the machine is deceased is prevented by an under-voltage trip. This defensive assess is fitted when alternators are arranged for equivalent operation. On the spot the operation of the trip is necessary to prevent closure of the breaker. However an under-voltage trip also gives protection against the loss of voltage while the machine is connected to the switchboard.
Tripping in this case must be delayed for discrimination purposes, if the voltage drop is caused by a fault.
Then there is a time allowed for the particular breakers to recover voltage without any loss of power supply to the other working loads and again start its operation or become in a working condition.
RECTIFIER:
Performance Specifications:
Model----------------------------------------------------506
Input voltage-------------------------------------------440 volts
Input line variation------------------------------------±5%
Frequency----------------------------------------------50Hz
Efficiency-----------------------------------------------95% typical
Power Factor------------------------------------------0.90 at full output
Current Regulation----------------------------------0.5%
Dynamic Response---------------------------------1 cycle
Correction Time--------------------------------------6 cycle maximum - - with output filtering (10% to 90% step load)
Ambient Temp---------------------------------------40 ° C
Humidity--------------------------------------------95% non-condensing
Rectifier Circuit:
A wye(Y) connected secondary; ANSI/IEEE C57.18.10 circuit No. 23 is used. Output rectification and regulation is accomplished using thyristors (SCRs).
Ripple:
5% RMS AC ripple at full rated current, when operating at 25% to 100% output voltage.
Cabinet:
The rectifier cabinet is constructed of all steel material according to NEMA1 standard, in the metal is pre-heated with a phosphate coating and finished with a power coated point to resist the corrosion, damage or scratching.
Thyristors:
The thyristors (SCRs) are rated for continuous full load operation. In the unlikely event of a device failure, an optional auxiliary sensing circuit will detect a phase current imbalance and shut down the DC power to prevent the overload of remaining devices.
The thyristor assembly is designed for a maximum junction temperature not to exceed 80% of the maximum rated junction temperature of the device, to prolong the life of the device.
The peak inverse and forward voltage ratings of the devices are at least 2.5 times the peak voltage of the AC supply.
The devices are mechanically clamped and mounted to an extruded heat sink in a manner which insures less than a 10° C difference between the device and the heat sink.
The heat sink is designed to provide proper cooling and to limit the maximum temperature rise to 40° C. This design is in conjunction with the appropriate air CFM maintained on the heat sink. The heat sink is machined to exceed thyristor manufacture specifications.
Transient voltage surge suppression limits the maximum transient voltage to less than 2.5 times the peak inverse voltage of the device. This protects each device from surges caused by switching and other alternating current variables.
Primary Protection:
Primary protection is provided by means of an AC thermal magnetic circuit breaker with industry standard AIC ratings. An optional fast-acting AC current imbalance circuit is available, which shuts the rectifier down under a fault condition.
Cooling
Air Cooled Units: Cooling is accomplished by circulating ambient air across the heat generating components with axial fans. Optional NEMA 4X rectifier enclosure features an air conditioning system.
Water Cooled Units: Heated air from power semiconductors and main transformer is drawn into an air-to-water heat exchanger. Thermal transfer effectively reduces the air temperature, and then circulates the cooled air back into the semiconductor and transformer areas. An internal thermostat is adjustable to maintain the water cycle for proper cooling, while minimizing internal condensation. Direct water-cooled semiconductor designs are also available and can help lower the component ratings. This method of cooling insures long rectifier life for extreme operating environments. For either water-cooled design, the recommended water temperature range is 75° F to 85° F.
DC Output:
The DC output of the unit is isolated. Either the positive or negative terminal may be grounded. The obtained DC output voltage is 220 Vdc.
Control Panel:
A local control panel is located on the front door of the rectifier and includes output voltage and current analog meters, AC on and DC on indicator lights, start/stop/power off push buttons, output voltage and current control potentiometers, a voltage or current regulation mode switch, and a voltage or current limit control potentiometer. As an option, a NEMA 12 remote control panel can be provided.
Controls and Monitoring:
MICROPROCESSOR BASED CONTROL SYSTEM
A microprocessor based control system is used to provide accuracy, repeatability and programmable features.
CONSTANT VOLTAGE CONTROL:
Constant voltage control maintains the preset output voltage constant to within +0.5%. An adjustable maximum current setting limits the output of the DC power supply to a safe level and protects the system from an overload condition.
CONSTANT CURRENT CONTROL:
Constant current control maintains the selected output current constant to within +0.5% over a voltage range of 10% to 100%, with varying input voltages and loads. If the load is removed, the output voltage will rise to a preset limit value.
DC OVERLOAD:
A digitally enhanced overload circuit allows the selection of zero (0), one (1), two (2), or three (3) restart attempts once excessive output current is detected. Upon overload detection, the circuitry will disable the DC output, ramp the output back to its set level within five (5) seconds and continue operation without interruption as long as the excessive load has cleared. Upon exceeding the selected number of restart attempts and if the excessive load has not been cleared then the unit will shut down. The overload level is factory adjusted for 5% over the unit's rated current output.
Optional Controls and Monitoring:
PHASE IMBALANCE PROTECTION:
Fast-acting AC current imbalance circuitry is available. If imbalance limits are exceeded, the DC power will be shut off to prevent potential overload conditions.
OUTPUT RAMPING:
Automatic ramping (slope) is digitally controlled to ramp the DC output to a preset voltage or current setting, at an adjustable rate. One (1) of two (2) standard timeframes may be selected. The first timeframe is zero (0) to two (2) minutes, and the second is zero (0) to twenty (20) minutes. Optional longer timeframes are available. Ramping can be controlled via potentiometer settings, or an internal or external PLC.
AUTOMATIC AVERAGE CURRENT DENSITY CONTROL:
The AACD (Automatic Average Current Density) option is used to automatically control the rectifier's DC output voltage and optimize paint usage in e-coat applications. The AACD insures that the proper voltage levels are applied to the paint tank based upon the size of the part being painted, eliminating the need for manual voltage adjustments.
