Instrumentation And Metering

Question 1

What is the purpose of the OA circuit

Answer 1

• Is a return path where the CT secondaries are “commoned” in a wye circuit.
• Allows for a return path in case act secondary circuit is open.
• Also a return path for imbalances

Question 2

What is the purpose of the SCADA transducers

Answer 2

• Changes analog quantities to a usable value for the SCADA RTU.
• CT and PT secondary values are converted to low energy DC quantities that are safe for the RTU

Question 3

What are typical transducer inputs/ quantities

Answer 3

• Bus KV
• amps
• MW
• MVAR
• temperature
• line potential
• frequency
• tap positions

Question 4

How do SDADA transducers work, and what are their outputs

Answer 4

• Analog quantities go into the transducer (0-1 mA) and are converted to a 0-5VDC output across a 5k Ohm resistor.
• That output is then sent to the RTU and it converts them to a 0-2000 count signal.
• At the control center, it is converted back into an analog signal.

Question 5

Where are SCADA transducers located

Answer 5

Usually located in the basement panel near the HMA interposing relays.
-New shark meters have transducers built in.

Question 6

Explain the difference between the MW and MVAR instruments and meters

Answer 6

There is a 90-degree phase shift on the MBTA are meters from that of the MW meters. This is achieved by using a phase-shifting autotransformer onto element meters

Question 7

What is the location of the o a circuit

Answer 7

The OA circuit comes from the Nexus point for various CT secondary circuits. It is connected to the ground Grid at the first terminal block it encounters inside the control house. The circuit is routed through a make before break to test switch that allows the CT to be shorted at that point sending audio

Question 8

Explain Blondell’s theorem

Answer 8

An element in a watt or VAR meter includes the voltage and current coils. The number of elements required for a watt or VAR meter to correctly measure the Watts and VARs in a circuit depends on how many wires are in the circuit. According to Blondell’s theorem, 1 measuring element is needed for each wire in a circuit. However if one wire is used as a common point to connect all the potential coils of the elements together then one less element is needed. Examples, a 3-phase 3 wire circuit requires two elements. A 3-phase 4-wire circuit requires three elements

Question 9

Explain the term telemetered

Answer 9

Measuring, transmitting, and receiving device used in telemetry

Question 10

Blame the term telemetry

Answer 10

Telemetry is the wireless transmission and reception of measured quantities for the purpose of remotely monitoring system conditions or system parameters. Also used in reference to signals that contain such

Question 11

List the precautions that should be used at Major stations in your District when looking for a DC ground if you need to power down the BETA unit

Answer 11

• When the BETA unit is powered down, the substation operator will lose indications of alarms on the SER and logger and control of the mouse, keyboard, alarm control panel, and howler.
• The ADF will still show alarms with the red LEDs. Inform dispatch that you’re powering down the beta unit and ask them to call you if they receive any alarms hello.

Question 12

List of precautions that should be used at Major stations in your District when looking for a DC ground if you need to power down the annunciator system

Answer 12

• Shutting down will cause the dispatch and local alarms to be lost for the duration.
• Take the station RTU to local to back page nuisance alarms to dispatch.

Question 13

List of precautions that should be used at Major stations in your District when looking for a DC ground if you need to power down the SDADA rack

Answer 13

• Consult with PSC prior to powering off the rack.
• All indications, quantities (including to AGC) and SCADA will be lost
• take the station RTU to local and inform the AGC dispatcher to dummy and quantities

Question 14

List the precautions that should be used at Major substations in your District when looking for a DC ground if you need to power down PCB trip circuits

Answer 14

Bypass and isolate the PCB prior to opening the PCB trip bus ACB

Question 15

Describe any non-billing outputs from RMS units in your District

Answer 15

For the RMS remote unit when an alarm is received, the RMS will output the alarm to MV99 PC at dittmer
-the two alarms that are outputted are critical or non-critical

Question 16

Describe any non billing outputs for the RMS units

Answer 16

RMS Unit can have remote alarm outputs there are usually two.
-one critical and one non-critical alarm that are sent to Dittmer.

Question 17

Explain the steps and operator should take if they find control panel a phase a meter reading zero, B&C phases read 600a each

Answer 17

• Check the log book for recent work.
• Check knife switches at bottom of the panel.
• If it is an analog meter you can tap the meter to see if it is stuck.
• Consult with SPC/SM and Trace out the circuit

Question 18

Explain the steps an operator should take if a selective voltmeter reads zero on one position and normal voltages on all the other positions

Answer 18

• Cycle the switch a few times.
• Use a digital multimeter to measure the input if possible.
• Carefully inspect the PT.
• Consult with SPC SM and Trey circuit

Question 19

Explain the steps in operator should take if a hotline indication does not illuminate when the associated line is energized

Answer 19

• Check the light bulb.
• Is the system in a configuration that removes the PT supplying the hotline (a bypass).
• Check for proper indication using the sink scope.
• Carefully inspect the PT/CVT.
• Consult with SPC/SM

Question 20

Explain the steps and operator should take if a line positions and meter at an unattended substation is pegged off the scale explain how the actual load current can be determined.

Answer 20

• Check the microprocessor relays if present for current.
• Check metering equipment if available.
• Call dispatch to confirm quantities.

Actual load current can be determined by using the power triangle and Ohm’s law to calculate amps

VA² = W² x VAR² to find VA
VA/V = A

Question 21

Explain how to cut out and restore a JEM meter

Answer 21

• If the meter is redundant with a toggle switch for A or B, use that to switch to the meter not being cut out prior to cutting out the JEM meter.
• Use prints to find the correct panel and Knight switches.
• Backseat currents first then cut out potentials.
• To restore reverse the procedure

Question 22

Explain how to cut out and restore a JEM meter with EXJ register

Answer 22

• These meters output quantities to AGC, consult a AGC before cutting out the meter.
• If the meter is redundant with a toggle switch for A or B, use that to switch to the meter not being cut out prior to cutting out the JEM meter.
• Backseat the currents first, then cut out the potentials.
• To restore follow the procedure in reverse