Data rate etc: 9600baud, no parity, 8 data bits, 1 stop bit
Protocol: Modbus RTU, A30 acting as slave, SCADA system acting as master.
Slave Number: 1
Supported Modbus
Function Codes: Function Code 3 – Read Holding Registers Function Code 6 – Write Holding Registers 12.2 Physical Connections
Front Connector: COM1 - 9 way male D type connector on front of control card provides isolated RS232C requiring the following connections:
Pin 2 – receive data Pin 3 – transmit data Pin 5 – 0V
No handshaking is required.
Rear Connector: 25 way female D type connector on rear panel of the controller provides isolated R S232C requiring the following connections:
Pin 3 – receive data Pin 2 – transmit data Pin 7 – 0V
No handshaking is required.
12.3 Data Available
See 19 Appendix C - Holding Registers For SCADA, Page 122
13 TRANSDUCER CALIBRATION PROCEDURE
Note: The A30-CON and A30-MON card transducers are calibrated at the factory prior to despatch and will not normally require adjustment. Any slight discrepancy between the values indicated on the HMI and panel instruments is more likely to be due to panel meter error rather than AVR error. Where a replacement card is fitted to an existing installation, it may be necessary to check calibration of the card in the mainframe, and in this case, measurements should be made using calibrated instruments with accuracy better than ±1%.
13.1 Line Voltage Calibration On The A30-CON Card 1) Open mainframe switch SW1.
2) Insert the A30-CON card into the extender card and plug them into the correct mainframe position.
3) Close SW1.
4) Plug the Comms link into the connector marked `COM 2' on the A30-CON front panel.
5) With the machine running at rated speed, select `Standby' control and adjust the line voltage to nominal.
6) Use the HMI to indicate sensing voltage and note the reading. Check that the indicated value ie equal to the average value of the three mean line to line voltages applied to the terminals 139, 140 and 141 when measured with a high accuracy (better than ±1%) mean (average) responding voltmeter.
If necessary, adjust RV5 on the control card if calibration is required.
If the AVR is set to measure single-phase line voltage, the value displayed on the HMI should correspond to the average line voltage supplied to terminals 140 & 141.
13.2 Field Current Calibration On The A30-CON Card
Use the HMI to display exciter field current and check that the value indicated on the display is equal to that indicated on the panel field ammeter. If necessary, the transducer can be calibrated against an ammeter with accuracy better than ±1% by adjusting RV3 on the control card.
13.3 Line Current Calibration On The A30-CON Card
Load the machine in standby control to give approximately 80% rated line current (MW or MVAr).
Use the HMI to display line current and check that the value indicated on the display is equal to that indicated on the panel line ammeter. If necessary, the transducer can be calibrated against an ammeter with accuracy better than ±1% by adjusting RV4 on the control card.
13.4 Temperature Transducer Calibration on the A30-CON Card
1) In the first instance, check that the temperature displayed on the HMI corresponds to the ambient temperature of the RTD.
Check that the temperature compensation is specified on the QC.48 document and that an RTD measuring `generator inlet air temperature' is connected to the AVR. Use the HMI to display temperature and confirm that the indicated value corresponds to the generator inlet air temperature in the location of the RTD.
2) The temperature transducer can be calibrated using 100Ω and 115Ω resistors (accuracy
±1%) as described below:
a) Trip FSC, and open SW1 in the mainframe. Connect the 100 Ω resistor across terminals 116 and 117. Link terminals 116 and 118. Fit the A30-CON card into the extender and insert in the mainframe. Close SW1 in the mainframe. Use the HMI to check that temperature compensation software is enabled. If it is turned off, confirm that temperature compensation is required and if so, turn the software on.
Set the HMI to indicate temperature and adjust RV1 on the control card so that the dc voltage between C2/4 and C2/11 is zero.
Adjust the dc voltage at TP7 wrt TP1 to 1.0V using RV6. Adjust the temperature display on the HMI to 0°C using RV2.
b) Open SW1 in the mainframe. Replace the 100 Ω test resistor by the 115Ω resistor.
Close SW1 and check that the HMI now indicates 40°C ±2°C and TP7 wrt TP1 is 5V.
c) If the temperature reading is not correct adjust RV6 for range and RV2 for level.
13.5 Line Voltage Calibration on the A30-MON Card
The procedure is the same as Section 13.1, except that this is carried out on the A30-MON card.
13.6 Field Current Calibration on the A30-MON Card
The procedure is the same as Section 13.2, except that this is carried out on the A30-MON card.
13.7 Line Current Calibration on the A30-MON Card
The procedure is the same as Section 13.3, except that this is carried out on the A30-MON card.
13.8 Temperature Transducer Calibration on the A30-MON Card
The procedure is the same as Section 13.4, except measurements and adjustments of RV6 and RV5 are made on the A30-MON card.
14 STEP RESPONSE TESTING
14.1 Step Response
Step response testing involves the sudden application of a step increase or reduction to the regulator set point. This causes a disturbance in the output of the regulator that is reflected to the output of the machine. The resulting transient provides information about the damping of the regulator and is helpful when optimising the settings of the stability controls.
Step response testing is carried out in the following circumstances:
Ø when the machine is running on open circuit when setting up the stabilising, in this case a step up of 5% is recommended.
Ø When the machine is running in parallel with the supply and it is required to test the response of the under excitation limiter. In this case a step down of 2% maximum is recommended.
Ø when the machine is running in parallel with the supply and it is required to test the response of a power system stabiliser. In this case a step down of 2% maximum is recommended.
When line current greater than 0.1 per unit is present the maximum step is limited to 2%
The reference automatically returns to normal 20 sec after the step is applied.
14.2 Step Response on Open Circuit
Before starting any step response tests, first confirm that no equipment connected to the generator is likely to be adversely affected by the tests.
Initially confirm that the test step size is set to the required level in the maintenance presets on the HMI. A step of 5% is recommended.
It is recommended that the line voltage is initially set 10% below nominal until the stabilising controls have been adjusted so as to reduce voltage overshoot during the response test. The machine voltage may be increased to nominal when the settings are close to optimum.
The HMI displays the overshoot, undershoot and recovery time. Each time a step response test is enabled, the previous values are destroyed.
The shape of the voltage transient may be viewed in the trending display although this is unsuitable for taking accurate readings.
It is recommended that the step be allowed to time out for 20 sec, before returning to nominal voltage.
14.3 Stabilising Adjustment.
The step response of the system may be optimised by adjusting the proportional (P), integral (I) and differential gain (D) by accessing the maintenance presets menu.
The Integral Gain, when set correctly, has very little effect on the transient response and should be set initially to 100.
In general increasing the Proportional Gain will give faster rise time but too much will give a response which is difficult to damp out and probably a large overshoot.
Damping can be improved and overshoot reduced by increasing the Differential Gain however, too much will give poor rise time and may cause fluctuations in the exciter field voltage.
The HMI shows the value “Mark – Angle” and this is an indication of the variation of the thyristor firing angle. Under steady state conditions Mark should be almost constant, and Mark – Angle will display the variation in the firing angle which should not normally exceed 10% of the late firing limit. If this does occur it is recommended that the Differential Gain is reduced.
Integral Gain (I) will cause instability if too low typically less than 30. Instability depends on (P), but if (P) is less than 60 then (I) will need to be higher, typically 500 for P = 35 on turbo generators. Too high a value will give poor regulation and long rise time.
The following table of stabilising settings is a general guide:
Table 26: Stabilising Settings
Typical Ranges Typical Salient Pole Typical Turbo Generator
P 20 – 100 50 50
I 100 – 200 100 100
D 20 – 100 40 40
The contract settings in the QC.48 document provide a good starting point. If after a 5% step the overshoot is too high, increase the Differential Gain to reduce the overshoot. If the Differential Gain is unusually large it may be better to reduce Proportional Gain to reduce the overshoot. The effect of this will be to reduce the rise time.
If the line voltage is oscillatory the Integral Gain may be too low (do not reduce below 100) Use the 5% step to optimise the overshoot to about 15% -30% of the 5% step size. The under shoot should be much less than the overshoot, typically 0% to 6% of the step size.
In the majority of applications, an adequate response with minimal overshoot can quite easily be achieved using step response testing on open circuit and the facilities on the HMI. If the application requires the best possible response this will necessitate recording equipment and possibly load application and rejection testing.
14.4 UEL Stabilising
Adjustable Proportional, Integral, and Differential gains controls have been added to the under excitation limiter. It is recommended that they are set initially to I = 50, P = 20, D = 20.
When setting up the UEL response, steady state stability should initially have been proved by running at zero power and slowly reducing the set point of the AVR until the under excitation limiter turns on.
The response of the Under Excitation limiter may be tested by running the machine lightly loaded when in parallel and initiating a step down in AVR set point. The excitation will reduce and the machine will generate leading VArs. Check that the Under Excitation limiter turns on immediately with no appreciable overshoot in the leading VArs. It may be necessary to optimise the response by making adjustments to the UEL stabilising controls.
15 OPERATING PROCEDURES AND MAINTENANCE
15.1 Operating Procedures
It is important to study operating procedures for the generator and turbine/engine system which are beyond the scope of this manual. The following instructions should be followed to ensure correct operation of the AVR.
15.1.1 Application And Removal Of Excitation
It is important that the 'Excite' input should be energised only after the AVR Main Electronics Supply has been applied.
The typical A30 Excitation System Circuit Diagram (See Appendix E - Drawings) shows an external Excitation Isolator Switch SW1 and the Field Suppression Contactor FSC (driven by the “Excite” input) within the AVR.
The excitation isolator should be provided for maintenance purposes and should be left closed except during maintenance and commissioning.
The majority of applications for this AVR are designed to be fully automatic. In this case the “Excite” input should be energised using a speed detector switch, external to the AVR, which should be set to switch at 80% rated speed.
On shut down the speed switch should remove the 'Excite' signal on speed reduction, and a 'Suppress' signal should be given before the AVR power supply is removed.
When it is a requirement for an operator to manually apply and remove excitation, a switch to apply and remove the 'Excite' input (closing and tripping the field suppression contactor FSC) should be fitted to the control panel.
The PMG isolator should not be used to apply excitation, as its closure when the field contactor is already closed does not allow an adequate initialisation period for the AVR and may occasionally cause a malfunction.
15.1.2 Parallel Running / Single Running
Power factor or VAr Control is provided for generator operation in parallel with a power system. These functions should be selected only when the paralleling circuit breaker is closed. Power Factor or VAr control should not be selected on a single running generator.
15.2 Maintenance
The A30 Excitation Controller is completely solid state, apart from relays, contactors and switches, and requires very little maintenance. It is recommended that the AVR is inspected approximately every 12 months to check for excessive dust build-up, and that all relays, fuses and connections are secure. Excessive quantities of dust should be removed with a soft brush.
In common with generator protection systems, it is good practice to annually check the calibration and the correct operation of all the various functions of the AVR because some (monitors or limiters) may never have needed to operate since the equipment was installed.
This entails making checks that are carried out during commissioning and, if required, Brush Service Department can provide this service.
WARNING: Take anti-static precautions when handling cards. Ensure that you are earthed (grounded) by using a wrist strap or similar device. An earth connection terminal is fitted in the centre or the front right hand mounting bracket of the AVR to which a wrist strap may be clipped.
Electronic cards can be damaged by static discharge and should be carried in anti static protective containers wherever practicable. They should always be stored and transported in anti static bags or boxes.
16 FAULT FINDING
Note: The advice given in the safety notice at the front of this Instruction Manual should be followed when fault finding.
16.1 General Information
If the AVR does not function correctly, a test sequence is recommended in which the generator and external wiring are first thoroughly checked before it is assumed that the fault lies in the electronic equipment. The faultfinding procedure is designed to enable faults to be found quickly. It is essential therefore, to follow the order in which they are presented.
In the event of finding a fault on any part of the AVR the company strongly recommends that no attempt is made to repair the unit, but that it is replaced by a spare which should be re-commissioned according to the relevant section of this Instruction Manual. The faulty unit should be returned to the Works for repair quoting the relevant Type/Model and Contract No's, together with the nature of the fault.
16.2 Precautions
Meggers, flash testers and bell sets must not be used to check any equipment connected to, or incorporating semi-conductors.
If these devices are to be used to check the wiring to the AVR, first disconnect all cables to the AVR.
WARNING: Take anti-static precautions when handling cards. Ensure that you are earthed (grounded) by using a wrist strap or similar device. An earth connection terminal is fitted in the centre or the front right hand mounting bracket of the AVR to which a wrist strap may be clipped.
Electronic cards can be damaged by static discharge and should be carried in anti static protective containers wherever practicable. They should always be stored and transported in anti static bags or boxes.
16.3 Procedure
16.3.1 Preliminary Checks
Before commencing fault finding on the AVR unit, the following preliminary checks should be carried out:
a) Check correct operation of the generator, ie. PMG output available (if applicable), the field and sensing signals are correct etc.
b) Check all wiring associated with the excitation system.
c) Check all contactors, switches and other external components associated with the AVR unit.
d) Check that all the correct links are fitted in the AVR as detailed in the contract QC.48 document.
e) Check all fuses and replace any that have failed. Fuse ratings are given in Section 6.
16.3.2 AVR Checks
Having completed these preliminary checks, if the problem remains, the cause may be assumed to be internal to the AVR, or in its setting up. In this event the problem will generally fall into one of the following categories:
1) A30-CON card Faults - see Fault Finding Table 1 2) A30-MON card Faults - see Fault Finding Table 9 3) Utilities Card Faults - see Fault Finding Table 15
4) Standby Control Card Faults - see Fault Finding Table 23 16.3.3 Thyristor Check
The Main and Standby power circuits are single-phase half-controlled rectifiers each comprising two diodes (in a single module) and two thyristors (in a single module). The thyristors can be checked in situ with the aid of a battery, ammeter and two resistors, after isolating the AVR and temporarily removing the relevant semi-conductor fuse (FS5 or FS6) and unplugging plug Q from the Backboard.
A
15 Ohm 12 W
15 Ohm 0.5 W 12 V Battery
1 Amp Short Term Rated
Switch
Gate
Thyristor Under Test
Anode
Cathode
Figure 24: Thyristor Test Circuit
1) Initially, with switch S open and not having previously been closed, ensure that the ammeter registers zero current.
2) Close S and observe that the ammeter now registers approximately 0.75A.
3) Re-open S and observe that the ammeter continues to register - ideally as in 2) above.
If any of these three tests is not satisfied for either positive or negative arm thyristors, then the thyristor module should be replaced.
Note: To reduce the current to zero after the thyristor has been triggered, as in 2) above; the battery circuit must be disconnected.
16.4 Fault Finding Tables
NOTE: In the following tables where reference is made to Test Point 1 (TP1) on the A30-CON and MON cards, use TP1 on the main body of the card, not TP1 on the A30-M188.
Description Page No.
Fault Finding Table 1: A30-CON Card Faults 92
Fault Finding Table 2: Instability In Main Channel Control On Open Circuit 93 Fault Finding Table 3: High Excitation Or Voltage On Open Circuit 94 Fault Finding Table 4: Low Excitation Or Voltage On Open Circuit In Main
Control Channel 95
Fault Finding Table 5: Main Control Channel Temperature Compensation
Error 96
Fault Finding Table 6: Main Control Channel Field Current Measurement Error
96 Fault Finding Table 7: Incorrect Line Current/Phase Measurement 96 Fault Finding Table 8: Incorrect Frequency Measurement 96
Fault Finding Table 9: A30-MON Card Faults 97
Fault Finding Table 10: A30-MON Line Voltage Measurement Error 97 Fault Finding Table 11: A30-MON Field Current Measurement Error 98 Fault Finding Table 12: A30-MON Temperature Measurement Error 98 Fault Finding Table 13: A30-MON Line Current/Phase Measurement
Inaccurate 98
Fault Finding Table 14: A30-MON Frequency Measurement Error 99
Fault Finding Table 15: Utilities Card Faults 99
Fault Finding Table 16: Failure Of A30-CON And A30-MON Card DC
Supplies 100
Fault Finding Table 17: Failure Of ±15V A30-CON Card Supply (Other DC
Supplies Present) 100
Fault Finding Table 18: Failure Of ±15V A30-MON Supply (other DC
Supplies Present) 101
Fault Finding Table 19: Failure Of +5V A30-CON Card Supply (Other DC Supplies Present)
101 Fault Finding Table 20: Failure Of +5V A30-MON Supply (Other DC Supplies
Present) 102
Fault Finding Table 21: Diode Failure Indicator Faults 102 Fault Finding Table 22: General Alarm (LED5) Given On Utilities Card 103
Fault Finding Table 23: Standby Control Faults 103
Fault Finding Table 24: Standby Control Faults - No Excitation When
Running On Standby 104
Fault Finding Table 25: Standby Card Faults - Line Voltage Unstable When
Machine On Open Circuit 105
Fault Finding Table 26: Standby Control Faults - Machine Will Not Run In Parallel When Selected In Voltage Control Mode
Fault Finding Table 26: Standby Control Faults - Machine Will Not Run In Parallel When Selected In Voltage Control Mode