KCR-760 VOLTAGE REGULATOR FOR SR4 HV Caterpillar


Systems Operation

Usage:

Voltage Regulator Circuits

The voltage regulator senses the generator voltage, compares a rectified sample of that voltage with a reference voltage and supplies the field current required to maintain the predetermined ratio between the generator voltage and the reference voltage. The KCR-760 voltage regulator is designed for three phase sensing and includes two sensing transformers (T1 and T3). The sensing circuitry also includes a transformer (T2) and potentiometer (R4). Transformer T2, potentiometer R4, and an external current transformer provide means of attaining reactive kVA load sharing during parallel generator operation. The parallel operation components do not affect voltage regulator operation when the generator is operated singly.

Underfrequency limit (UFL) or V/Hz option circuitry interacts with the regulator sensing and error detector in a manner that decreases voltage during underspeed operation. A solid state flashing circuit operates each time the generator is started. The flashing circuit de-energizes when generator voltage has built up to about 70 percent of rated voltage output. Most of the circuits are contained on a printed circuit board. Parts that are individually mounted on the regulator case are the sensing transformers, parallel operation transformer T2, parallel voltage droop potentiometer R4, the power stage, and a fuse. External voltage adjust rheostat VAR is provided for installation on a control panel.

Sensing Circuit During Single Generator Operation

The voltage sensing transformers provide a voltage proportional to the generator voltage output. This voltage is fed through the secondary of T2 to a full wave rectifier comprised of silicon diodes D3, D4, D17, D18, D23, and D24. The rectified voltage is filtered by resistor R3, choke L1 and capacitor C1. The dc signal from the filter is applied to the error detector and the underfrequency limit.

Shorting the secondary parallel operation transformer T2, either by using the jumper bar across CT1 and CT2, or turning R4 to its full counterclockwise position or setting the UNIT/PARALLEL switch to UNIT position, eliminates the effect of T2 during single generator operation.

Sensing Circuit During Parallel Generator Operation In Reactive Voltage Droop Compensation Mode

Generators interconnected for reactive voltage droop compensation will proportionally share inductive reactive loads during parallel operation by a decrease in generator system voltage. This method of kVAR load sharing is described in the paragraphs that follow.

The sensing transformer provides a voltage proportional to the sensing voltage. A current transformer (CT) installed in line 2 of generator develops a signal that is proportional in amplitude and phase to the line current. This signal develops a voltage across the slide-wire parallel voltage droop adjust potentiometer R4. The tap on R4 supplies part of this voltage to the primary of transformer T2.

The voltage developed in the secondary of the sensing transformer and the voltage developed in the secondary of T2 add vectorially. This action provides a voltage to the sensing diodes that is the vector sum of the stepped down sensing voltage and the parallel current transformer signal through T2. The sensing rectifier dc output is filtered and applied to the error detector and underfrequency limit.

When a resistive (unity power factor) load is connected to the generator, the voltage that appears across the droop potentiometer leads the sensing voltage by 90 degrees, and the vector sum of the two voltages is nearly the same as the original sensing voltage; consequently, almost no change occurs in generator output voltage.

When lagging power factor (inductive) load is connected to the generator, the voltage across the droop potentiometer becomes more in phase with the sensing voltage, and the combined vectors of the two voltages result in a larger voltage being applied to the sensing rectifiers. Since the action of the regulator is to maintain a constant voltage at the sensing rectifiers, the regulator reacts by decreasing the generator output voltage.

When a leading power factor (capacitive) load is connected to the generator, the voltage across the droop potentiometer becomes out of phase with the sensing voltage and the combined vectors of the two voltages result in a smaller voltage being applied to the sensing rectifiers. Then the regulator reacts by increasing the generator voltage.

During parallel operation of two or more generators interconnected for reactive voltage droop, if field excitation on one of the generators should become excessive and cause a circulating current to flow between the generators, the circulating current will appear as an inductive load to the generator with excessive excitation and a capacitive load to the other generator(s). The parallel components R4 and T2 will cause the voltage regulator of the generator with excessive field excitation to decrease the generator voltage while the voltage regulators of the other generator(s) will increase the generator voltage.

Sensing Circuit During Parallel Generator Operation in Parallel Cross-Current Compensation Mode

Parallel cross-current compensation allows two or more parallel generators to share inductive reactive loads with no droop or decrease in the generator system output voltage when the line currents are proportional and in phase. This is accomplished by the action and circuitry described previously for parallel reactive voltage droop compensation and the interconnection of the current transformer secondary in a closed series loop. Circulating currents cause the system to react as described previously for parallel voltage droop compensation.

A unit/parallel switch connected in each generator system eliminates the series resistance of the CT's in shut down generator sets from the CT's of the generator sets that are operating.

Error Detector

The error detector circuitry consists of a voltage adjust circuit, a voltage divider, a two-stage differential amplifier, and an internal minor feedback filter. The voltage adjust circuit consists of an external voltage adjust rheostat VAR, a voltage range adjustment R2, and fixed resistor R1. Full travel of the external voltage adjust provides ± 10% adjustment of the generator output voltage from nominal. The voltage range adjustment R2 establishes the maximum and/or minimum voltage adjust limit of VAR. The voltage adjust circuit and a voltage divider consisting of resistors R5 and R71 determine the input signal to the first differential amplifier. The first differential stage is comprised of transistors Q1 and Q2, resistors R9 through R23, capacitor C3, Zener diode Z1, and circuitry within the underfrequency limit.

Underfrequency limit (UFL) provides a reference voltage to the base of the transistor Q2 as described in the UFL circuit description. During generator operation at rated frequency the reference signal is constant and identical to the Zener voltage. Voltage from the sensing circuit which is proportional to the generator voltage is applied to the base of transistor Q1. When Q1 base voltage is different from the reference voltage applied to the base of Q2, there will be difference in Q1 collector current with respect to Q2 collector current.

The current from the collector of transistor Q1 is divided by resistors R9 and R16 and injected into the base of the second stage differential amplifier transistor Q3. Similarly, the current from the collector of transistor Q2 is divided by resistors R14 and R15 and injected into the second stage differential amplifier transistor Q4. Resistor R10 and capacitor C3 help to prevent oscillations at high frequencies. The second stage differential amplifier amplifies the output of the first stage differential amplifier.

Components included in the second stage differential amplifier are transistors Q3 and Q4, and resistors R24 through R27. The collector voltage of transistor Q3 controls the phase control circuit. The minor feedback filter consists of resistor R8 and capacitor C2. The filter removes any remaining ac from the dc signal.

Phase Control Circuit

The phase control circuit consists of diodes D5 and D6, resistors R28 through R32, capacitors C6 and C7, Zener diode Z2 and programmable unjunction transistor (PUT) Q5.

The phase control circuit is a "ramp and pedestal" control that regulates the phase angle of the power controller circuit SCR's by controlling the "turn on" signal it supplies to the gate of the SCR's. An exponential ramp voltage that starts from a voltage pedestal provides the "turn on" gating signal. Because the ramp voltage starts from the voltage pedestal, a small change in the amplitude of the pedestal voltage results in a large change in SCR phase angle.

The amplitude of the pedestal voltage is determined by the collector current of second stage differential amplifier transistor Q3. Zener diode Z2 serves as a voltage clamp and resistors R31 and R32 are a voltage divider which determines the threshold of the programmable unjunction transistor Q5. The output of PUT Q5 is applied to the gate of the power controller SCR's through resistors R43 and R44.

Power Stage (Power Controller)

The power stage supplies the generator exciter field current. The power stage consists of an SCR/diode bridge rectifier. The power stage input is either single phase 120 V ac or single phase 240 V ac depending on regulator design. The output of the power stage is regulated by the "turn on" gating signal its SCR's receive from the phase control circuit. The circuit includes a free wheeling diode for field discharge of the inductive exciter field load and a fuse (F1) in its input power line.

Field Flashing Circuit

The flashing circuit includes the power stage SCR, field effect transistor (FET) Q6, transistors Q7 through Q10, resistors R34 through R46, diodes D7 through D11 and capacitor C8. Transistors Q8 and Q9, and resistors R34, R36, R37, R38, R40 and R41 comprise a Schmidt trigger circuit. The Schmidt trigger turns on when an increasing voltage is present with magnitude approximately 70% of the nominal 24 V dc output of the sensing rectifiers, and turns off when a decreasing voltage is present with magnitude of approximately 30% of the nominal output of the sensing rectifier.

When the Schmidt trigger is off, FET Q6 is on. This action turns on transistors Q10 and Q7 which supply current to fire slave SCR1 located on the circuit board. Slave SCR1 fires the silicon controlled rectifiers SCR1 and SCR2 in the regulator power controller circuit which, when on, supply current to the exciter field. When the Schmidt trigger turns on, FET Q6 turns off. This action turns off transistors Q10 and Q7 which removes the gating signal to slave SCR1 and in turn the gating signal of the flashing circuit from the power controller SCR's.

Stability Control

The stability circuit is a rate feedback RC network. It consists of capacitors C4 and C5, resistors R7, R19 and R20, and stability adjust potentiometer R6. This RC network injects a stabilizing signal from the regulator output which helps to prevent generator voltage oscillation.

Underfrequency Limit (UFL)

The UFL provides a reference voltage to the error detector which is constant when the generator output frequency is higher than a predetermined limiting frequency. When the generator is operating slower than the predetermined UFL operational threshold, the UFL will provide the error detector with a reference voltage that is proportionally lower.

The reference voltage to the UFL is supplied by Zener diode Z1. The UFL operational threshold for standard 50 and 60 Hz KCR-760 regulators are 49.5 Hz for 50 Hz application and 59.5 Hz for 60 Hz application. The operation of the various components comprising the UFL assembly is described in the paragraphs that follow.

The voltage from the sensing transformer is rectified by diodes D19 and D21 and the rectified signal is applied to a Schmidt trigger consisting of operational amplifier IC2A, and resistors R47 through R51. A 24 V dc peak-to-peak square wave is generated at the output of IC2A at double the frequency of the sensing voltage.

The 24 V dc square wave from the schmidt trigger is fed to the first stage of a two-stage monostable multivibrator where it is decreased to a 5 V dc peak-to-peak square wave at double the frequency of the sensing voltage. The 5 V dc square wave is applied to the second stage of the monostable multivibrator. The monostable multivibrator output pulse is uniform in amplitude and duration for each input pulse. Thus, the average voltage level of the collective pulses at the output of the monostable multivibrator is directly proportional to the frequency of the pulses. The monostable multivibrator output is fed into a four-pole Butterworth low pass filter comprised of operational amplifier IC2B and IC2C, resistors R60 through R66, and capacitors C13 and C18. This filtering circuit does the actual averaging of the collective pulses from the monostable multivibrator. Amplifier gain is set at level where its output equals the Zener reference at rated 60 Hz operation by resistors R65, R66 and capacitor C16. Where operated at rated frequency of 50 Hz, the circuit is set for 50 Hz operation by removing jumper J1. This action adds R57 to the circuit.

Diode D12 and integrated circuit IC2D form a voltage clamping circuit. If the voltage from the Butterworth filter is equal to that of the Zener reference, the UFL output to the error detector will be the same as the Zener reference and the UFL will have no effect on regulator operation. However, when the voltage from the filter decreases as occurs during underspeed operation of the generator, the reference voltage applied to the error detector is less than the Zener reference. This action will cause the error detector differential signal to proportionally increase in a manner that results in a proportionally later turn-on signal to the regulator output SCR's. The regulator then decreases excitation and a lowering of generator output voltage occurs.

A resistive network consisting of resistors R54 and R56 and potentiometer R55 determines the underfrequency limit operational threshold. Zener diode Z3 and capacitors C9 and C10 protect the integrated circuits from damage should excessive voltage spikes occur.

Installation

Mounting

The voltage regulator can be mounted in any position without affecting its operating characteristics. The voltage regulator is convection cooled. Sufficient space should be retained about the regulator for heat dissipation, making electrical connections and controls adjustments. The voltage regulator can be mounted in any location where shock and vibration is not excessive and the ambient temperature does not exceed its ambient operational limits.

Interconnection

The regulator must be connected to the generator system as instructed in this section and as shown in the connection diagram provided with the generator set. An overall outline drawing that shows the location of regulator mounting provision and identifies parts of the voltage regulator is contained in the "Wiring Diagrams" section in the end of this manual. Also contained in that section are typical interconnection diagrams and electrical schematics of the voltage regulator. Number 14 gauge or larger wire should be used for connections to the voltage regulator.

------ WARNING! ------

De-energize generator set starting circuit before making repairs, connecting test instruments or removing or making connections to or within the voltage regulator. Dangerous voltages are present at the voltage regulator terminal boards and within the voltage regulator when the generator set is running. These include the sensing voltage, power to the voltage regulator and the voltage regulator output. Accidental contact with live conductors could result in serious electrical shock or electrocution.

--------WARNING!------


NOTICE

Megger or high potential test equipment must not be used when testing the voltage regulator. Disconnect interconnecting conductors between the generator and voltage regulator when testing generator or exciter with megger or high potential test equipment. The high voltage developed by megger or high potential test equipment will destroy the solid state components within the voltage regulator.



NOTICE

Regulator sensing circuit must never be opened while power is applied to the regulator input power terminals. Loss of sensing voltage will result in maximum regulator output.


Three Phase 100-600 V ac Sensing (Terminals E1, E2 and E3)

Regulators are designed for three phase sensing and include two sensing transformers (T1 and T3) as shown on Figure 4.

The regulator sensing transformers will include multi-tap primary winding for use with the sensing voltages of 100 to 139, 200 to 228, 216 to 265, 375 to 458, 432 to 528 and 540 to 600 V ac. The transformer primary winding taps are identified with the corresponding nominal voltages which are 120, 208, 240, 416, 480, 600 V ac.

To obtain proper operation, the internal wire from voltage regulator terminal E3 must be connected to the correct primary winding tap on transformer T1, and the internal wire from voltage regulator terminal E2 must be connected to the corresponding primary winding tap on transformer T3. Electrical wires within the regulator connect to the sensing transformers secondary winding as shown on Figure 4.

Input Power (Terminal P1 and P2)

* Regulator is designed for 240 V ac ± 10% input power and 125 V dc maximum continuous output. Connect single phase 240 V ac power to terminals P1 and P2.
* Where regulating system is supplied with electromagnetic interference filters, connect as shown on the wiring diagram.

Output Power (Terminals F+ and F-)

* Be sure regulator output matches the generator exciter rating. KCR-760 voltage regulator designed for 120 V ac input is designed for 65 V dc maximum continuous output.

KCR-760 voltage regulator designed for 240 V ac input is designed for 125 V dc maximum continuous output.

* Correct polarity must be maintained between the regulator output and exciter field.
* Field resistance for 65 V dc regulator should not be less than 6.5 ohms while field resistance for 125 V dc regulator should not be less than 12.5 ohms.
* Field circuit should not be grounded and must not be opened or shorted during operation of the generator set.
* Because the regulator output leads are not connected to any part of the system except the exciter field, they are not filtered. To minimize conducted EMI the leads should be kept as short as possible and shielded. Effective shielding can be attained by routing both leads through 1/2 inch metal conduit. In general, not more than one or two feet of field leads should be unshielded. If the voltage regulator is installed within the generator outlet box, it is possible to achieve satisfactory results with short unshielded leads.

Grounding

A good electrical power ground is not necessarily a good electromagnetic interference ground. Ground leads should be as short as possible, preferably of copper strap with a width of 1/5 the length. Grounding the chassis to earth ground makes all grounds common.

External Voltage Adjust Rheostat (Terminals R1 and R2)

Terminals R1 and R2 are provided for connection of the voltage adjust rheostat. The rheostat provides adjustment of the regulated generator voltage ± 10% of nominal. It is provided as a separate item for panel mounting. Connecting wires from the rheostat attach to terminals R1 and R2. A jumper wire must be connected between rheostat terminal 2 and rheostat terminal 1 as shown in Figure 2.

Connection to Reactive Voltage Droop Terminals CT, CT1 and CT5

Parallel Operation

Where generators will be operating parallel, install current transformer in Phase B from each generator and connect according to a or b that follows.

* Current Transformer (1 ampere secondary)

Connect secondary leads to CT* common and CT1. Be sure to maintain correct polarity. Make certain jumper, when supplied, is removed from across CT* and CT1.

* Current Transformer (5 ampere secondary)

Connect secondary leads to CT* common and CT5. Be sure to maintain correct polarity. Make certain jumper, when supplied, is removed from across CT* and CT1.

Reactive Voltage Droop or Cross-Current Compensation

The regulating system may be connected for parallel operation in either the reactive voltage droop or cross-current compensation mode. Connect according to either of the following.

* Reactive Voltage Droop

Connect the current transformer to the respective regulator as shown in Figure 8.

* Cross-Current Compensation

For cross-current, connect each CT to its respective regulator. Then connect the finish of the first CT to the start of the second CT, etc. Continue until all CT's are connected in series and connect the finish of the last CT to the start of the first CT (see Figure 8).

On parallel cross-current compensation applications consisting of two or more generators, a unit/parallel switch should be used if all the generators are not always on the bus. If the switch is not used, a voltage droop will be introduced into the system which will cause the voltage of the incoming generator to fluctuate prior to parallel. This is due to the unloaded generator parallel CT not supplying its compensating signal, but allowing a voltage drop to occur across it. Ideally, the switch is an auxiliary on the generator output circuit breaker that opens when the breaker is closed.

Generator Operating Singularly

When generators are not operating parallel and reactive voltage droop is not required, one of the following methods must be employed to eliminate the effect of the parallel operating transformer within the voltage regulator.

* Install unit/parallel switch across the current transformer secondary and close switch during single generator operation.
* Set voltage droop resistor R4 to its minimum droop position.
* Where generator will be operating singly, install jumper across terminals CT* and CT1.
50/60

UFL Circuit Hz Selector J1

The underfrequency limit components are V/Hz components are located on the voltage regulator circuit board, Figure 5. Parts comprising the UFL or V/Hz components are shown on Figure 7. A jumper wire J1 eliminates the effect of resistor R57. Removing the jumper J1 places R57 in the circuit.

* 60 Hz Operation

Make certain jumper wire is installed across marked J1. Wire is mounted on component side of circuit board and ends of jumper wire are soldered on foil side of the circuit board.

* 50 Hz Operation

Make certain jumper wire is removed from across area marked J1. Remove J1 by cutting each end of the jumper wire.

Voltage Regulator Fuse

The voltage regulator contains a 15 A normal blow fuse in the voltage regulator input power circuit (see Figure 1 and 4). In applications where voltage regulator power requirements are reduced, as when used with small generators where excitation is less than given, a smaller fuse may be used. Never install a fuse larger than 15 ampere and never install a delay type fuse.

------ WARNING! ------

Fire hazard can exist if voltage regulator fuse is larger than 15 A or delay type fuse is used.

--------WARNING!------

Accessory Items

Accessory items provided with the generator system must be connected as shown on the wiring diagram provided with the generator set and the accessory item drawing or instruction. The precautions and general procedures that follow should be observed when connecting accessory items.

NOTE: On generator systems that include the auto/manual voltage control option, the OFF position on the AUTO/OFF/MANUAL selector switch provides voltage shutdown. On generator systems that include a field circuit breaker, manually tripping the circuit breaker OFF provides voltage shutdown.

Voltage Shutdown (Engine Idle Switch)

The system can be equipped with a switch to allow removal of excitation in an emergency or when the prime mover must be operated at reduced speeds. This switch must be placed in the input power line to the regulator (terminals P1 or P2).


NOTICE

The voltage regulator dc output (terminal F+ and F-) must never be opened during operation. To do so will produce inductive arcing that could destroy the exciter or voltage regulator. Therefore, never place circuit breaker contacts in the exciter field circuit.


Field Circuit Breaker

The field circuit breaker must be of the type that has separate terminals for the trip element and the contacts. The circuit breaker trip element receives power from the field current. The trip element connects between the voltage regulator output and the exciter field.

EMI/RFI Suppression Package

Thyristor (SCR) type voltage regulators are by their nature producers of electrical switching noise, often called EMI (electro-magnetic interference) or RFI (radio frequency interference). The KCR-760 utilizes SCR switching. The EMI/RFI suppression package greatly reduces the magnitude of the noise transferred to the generator leads and radiated into the surrounding environment.

The EMI/RFI suppression package comprises a treated steel enclosure containing the following:

* The KCR-760 voltage regulator.
* A filter between the regulator voltage sensing terminals and the sensing voltage from the generator.
* A filter between the CT terminals of the regulator and the paralleling current transformer.
* The voltage setting potentiometer (accessible from outside the enclosure).
* A relay to permit exciting/de-exciting the generator from a remote location.
* Wire connection terminals.

A hole in the bottom of the enclosure, below the external terminal block, permits connection of a conduit for the wiring from the generator exciter field and PMG terminals.

It should be noted that the routing if the exciter and PMG wiring is an integral part of the design. The enclosure will accommodate a standard 12.70 mm (0.5 in) conduit connector. Use of steel conduit for the wiring to the exciter field and PMG terminals, over the entire distance, will assure compliance with the relevant RFI/EMI emissions requirements. Use of other materials must be evaluated for their shielding effectiveness.

Access to some of the connection terminals, as well as the KCR-76 itself, requires the cover of the enclosure to be opened. This is accomplished by removing the 13 screws securing it to the enclosure. A hinge at the left edge attaches the cover, but the screws are NOT captive. All 13 screws must be in place and contacting the cover to maximize the effectiveness of the suppression package.

Other than the KCR-760 itself, nothing within the EMI/RFI suppression package enclosure requires adjustment or calibration. The KCR-760 is a totally standard unit as would be supplied with a generator set with less stringent EMI/RFI requirements, all documentation for the standard KCR-760 is applicable. Replaceable parts are the filters, the relay, the voltage setting potentiometer, the diodes and resistor in the coil circuit of the relay, and the KCR-760.

Caterpillar Information System:

KCR-760 VOLTAGE REGULATOR FOR SR4 HV Application
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