Voltage Regulators

Outline Regulator Function & Purpose What is inside Neutral Position Nameplate Bypassing Basic Control Settings What is the function of a voltage regulator? To monitor voltage and maintain it within a preset range. “This workforce solution was funded by a grant awarded by the U.S. Department of Labor’s Employment and Training Administration. The solution was created by the grantee and does not necessarily reflect the official position of the U.S. Department of Labor. The Department of Labor makes no guarantees, warranties, or assurances of any kind, express or implied, with respect to such information, including any information on linked sites and including, but not limited to, accuracy of the information or its completeness, timeliness, usefulness, adequacy, continued availability, or ownership.” This work by Alpena Community College’s Sustainable Solutions for Northeast Michigan, a Department of Labor, TAACCCT funded project, is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

Voltage Regulator Function What is the function of a voltage regulator? The basic function of a voltage regulator is to monitor voltage and maintain it within a preset range. What is the function of a voltage regulator? To monitor voltage and maintain it within a preset range.

VLD = Voltage drop due to line losses End of line TRANS- FORMER VLD = Voltage drop due to line losses End of line VLD Voltage Distance

LOAD CURRENT VS TIME OF DAY CURRENT 12am 6am 12pm 6pm TIME OF DAY

How to Reduce Voltage Drop Change taps on distribution transformers Change taps of substation transformer Reconfigure system Install larger conductor Increase system voltage Install line capacitors INSTALL LINE REGULATORS Notes or Observations _______________________________________________________________

Voltage Regulators Purposes Primary Purpose Provide regulated voltage to meet power quality criteria Secondary Purposes Increase revenue Peak shaving Conservation voltage reduction Metering point Notes or Observations _______________________________________________________________

Power Quality What is the right voltage level? ±10% (132 to 108) Outage ±5% (126 to 114) Guideline ±2.5% (123 to 117) Customer expectation Notes or Observations _______________________________________________________________

Series Winding Shunt Winding ANSI TYPE B

Conventional two-winding transformer + + Vp = 1000V Vs = 100V - - 10:1

Step-Up Autotransformer + + Vs = 1100V Vp = 1000V - -

Step-Down Autotransformer + + Vp = 1000V - - Vs = 900V

Step Regulator + N + 1 2 3 4 5 6 7 - 8 -

Step Regulator with Revsersing Switch + N + 1 2 3 4 5 6 7 - 8 -

1.25% N 1 2 3 4 5 6 7 8 Non-Bridging

1.25% N 1 2 3 4 5 6 7 8 Bridging

TYPE B REGULATOR REVERSING SWITCH 1.25% SERIES WINDING L S N 1 2 3 4 5 6 7 8 CURRENT X-FORMER CONTROL SHUNT WINDING TYPE B REGULATOR CONTROL WINDING SL

Step Voltage Regulator Components The step regulator evolved as less costly device that could still maintain voltage within acceptable limits. Like the induction regulator, the step regulator has a shunt winding and a series winding. However, instead of having a moveable winding to induce a raise/lower voltage in the series winding, the shunt winding of a step regulator constantly induces a voltage in the series winding in the opposite direction, it utilizes a motor driven tap changer to change the regulator’s output, and employs a reversing switch that connects the series winding in the direction necessary to raise or lower the voltage. (Identify the bridging reactor for later reference.) Also note that the regulator shown here has only 4 taps, hence only 8 raise positions and 8 lower positions. The entire range of the regulator is raise or lower 10%. Each tap is worth 180 volts if connected to a 7200 volt source. Each step is therefore worth 90 volts. SHUNT WINDING

Voltage Regulator Connection in a Single-Phase Circuit Notes or Observations _______________________________________________________________

Regulator Neutral The regulator shown here is in the neutral position. The tap changer is at the neutral tap which has the series winding isolated from the load end and the reversing switch is open, isolating the winding from the source end. (Point this out on the slide.) 720V

Regulator Raise Operation When the regulator is called upon by it’s controller to raise the voltage, the motor starts moving the tap changer (clockwise as shown). This action also closes the reversing switch to connect the series winding in such a direction that the source voltage is added to the induced voltage. Note here that the tap changer has 2 contacts. This is necessary to keep from opening the circuit during a tap change. This would appear to short out a section of the series winding, and indeed this would be the case if not for the bridging reactor. The bridging reactor is a coil, connected across the leads of the tap changer and prevents the series winding from shorting out. This coil is center tapped and so connected to the load. As we see in the slide, the regulator has moved 1 step; 1 contact is on the #4 tap and the other is on the neutral tap. This is known as bridging. The #4 tap itself is worth 180 volts and that amount of voltage is place across the bridging reactor. With the load connected to the reactor’s center tap, only half of the #4 tap’s 180 volts are added to the source voltage.

Regulator Raise Operation If a further voltage increase is needed, the tap changer continues and makes another step. Both of the tap changer contacts are now on the #4 tap. Here, the bridging reactor sees no difference in voltage and the load current merely flows through both sides of the reactor with the full 180 additional volts contributed by the #4 tap.

And So It Goes And so it goes, on and on, picking up more of the series winding, until the desired voltage is reached or the regulator maxes out.

Picking up More Series Winding And so it goes, on and on, picking up more of the series winding, until the desired voltage is reached or the regulator maxes out.

Full Raise And so it goes, on and on, picking up more of the series winding, until the desired voltage is reached or the regulator maxes out.

To Lower Voltage If the regulator is called on to lower the voltage, the tap changer moves in the opposite direction to neutral. (Show tap changer on neutral tap and reversing switch open.

Regulator Lower Operation 7110V Note now that the reversing switch has now connected the source to the series winding in such a fashion that the source voltage and series are bucking each other. The tap changer has moved 1 step, bridging #1 tap and neutral, lowering regulator output by 90 volts. This continues on and on, one step at a time until the required voltage is reached or the tap changer reaches it’s limit.

Switching Checklist Putting Regulator In Service Check potential transformer settings.

Back Panel with Modular Terminals & Switches RCT2 RCT1 V6, V1, & C switches TB2 TB1 Optional FO-RS232 Board

BYPASSING Regulator Hazards The most hazardous thing to do with a regulator; BYPASSING BYPASSING

ABSOLUTELY, POSITIVELY A voltage regulator MUST be in the neutral position in order to “bypass” it while it is energized. A line/service technician must know how to operate the controls in order to maneuver the regulator into the neutral position. (READ SLIDE!)

AEP Safety Manual E 9.01 States: “Voltage regulators shall be placed in the neutral position, verified by two approved methods to be in the neutral and the control circuit made inoperative before they are bypassed. AEP Safety Manual (Revised July 15th, 2002) E 9.01 states; “Voltage regulators shall be placed in the neutral position, verified by two approved methods to be in the neutral and the control circuit made inoperative before they are bypassed.” Opinions from staff in AEP Safety are that in order to meet the requirements of “tested”, the Hastings RND will be used.

Voltage Regulator Neutral Position Mechanical Indication: Position indicator Position indicator. Center position of the indicating needle (or zero) is the neutral position. Clockwise from neutral is raise positions, counter-clockwise is lower positions. Point out also the range limit controls on the side of the enclosure.

Voltage Regulator Neutral Position Electrical Indication: Neutral light Indicating lights. The neutral light is an electrical indication of neutral position.

Hastings Neutral Detector Is a specifically designed voltmeter installed on a hot stick that measures the difference in voltage between the source and load conductors. This device is a specifically designed voltmeter with a digital readout that measures the voltage difference between the source and load sides of the regulator. It is used from the end of a hot stick and measures the difference in voltage between the source and load sides of the regulator. A regulator in the neutral position will result in a reading of “0” (zero) or near zero on the display.

Low impedance bypass loop Here’s what happens if a regulator is bypassed when not in neutral. You are trying to connect 2 conductors at different potential and that portion of the series winding being used shorts out. The shorted portion of the circuit is shown is green. When only a portion of the coil is connected, there is little impedance (a combination of factors that opposes current flow) that would tend to limit fault current. The fault current builds up rapidly. Tests at GE labs have observed currents of over 300 times the series winding’s rated capacity. The winding obviously cannot carry that much current and is destroyed. If you’re lucky, you’ll only burn the winding up. However, this internal damage has the potential for disastrous results including case destruction, switches welding shut, spectacular electrical displays, massive oil spills… The more windings in use (or the further the regulator is off neutral), the more impedance available, hence a greater restriction to fault current. Therefore, the worst possible tap position for an attempted regulator bypass is 1 step to either side of neutral.

Regulator Bypass Switches Non-sequenced Switch

Regulator Bypass Switches Kearney (sequenced switch)

Switching Checklist Taking Regulator Out Of Service Check position of regulator. Place regulator in the neutral position. Turn control to “off”. Verify neutral position. Disable control panel power source. Test regulator to be in neutral. Operate bypass switch as required depending on type of switch.

Bypassing - Remove Procedure Regulator Connected Line-to-Ground (GY) Source Load Phase A B S-DIS L-DIS S L Start 1 2 3 B O C S-Dis L-Dis SL Neutral Step 1 is Critical Operation.

Bypassing - Install Procedure Regulator Connected Line-to-Ground (GY) Source Load Phase A B L-DIS S-DIS Start 1 2 3 B C O S-Dis L-Dis S L SL Neutral Step 2 is Critical Operation.

Switching Checklist Putting Regulator In Service Check potential transformer settings. Check regulator in neutral and off position. Check power source disabled. Test regulator to be in neutral. Operate bypass switch as required. Enable control panel power circuit. Place regulator control to “automatic”.

When should a regulator be de-energized before bypassing? De-energizing When should a regulator be de-energized before bypassing? The regulator is inoperative and cannot be returned to the neutral position. Sometimes, regulators are inoperative and they just can’t be brought back to neutral. In these cases, there is simply no choice except to de-energize the regulator and take it out of service. The unit may have to be changed out or it may be possible to make repairs in the field. In either case, the regulator can be operated by an external low voltage power source and be placed in neutral prior to placing it back in service. The regulator cannot be insured to be in the neutral position.

As a lineman who operates regulators, here are some of the major external components with which you must be familiar. On the top left is shown a typical mechanical position indicator. The yellow needle indicates the position that the regulator is currently in. The silver hands on either side of the yellow needle are the “drag hands” which are shoved by the yellow position indicating needle and show the maximum raise and maximum lower levels that the regulator has operated to since they were last reset. Most drag hands are electrically reset by pressing a button in the regulator control. A few old regulators have drag hands which are reset by physically moving the hands back against the position indicating needle. On the bottom left is shown a position indicator housing and a black knob on the side. This is the range limit switch for the lower function. An identical switch exists on the opposite side for the raise limit. It is sometimes desirable to limit the range to which a regulator can operate. These switches are used for the desired settings. The photo on the right is one of a typical older style regulator control. These are being replaced across the AEP system with microprocessor controls but there are a lot of these still around. (Point out control knobs, test terminals, drag hand reset, neutral light, counter, etc…)

Another regulator unit. (Point out similarities.)

BASIC CONTROL SETTINGS Set Voltage Bandwidth Time Delay Control operating mode Reverse sensing mode Configuration System voltage (nominal) P.T. & C.T. ratios Line drop compensation Notes and Observations: _________________________________________________________

Set Voltage The voltage level (in 120V base) to which the control will regulate Settable for both forward & reverse power flow Forward set voltage = Function code (FC) 1 Reverse set voltage = FC 51 Default values are 120.0V Notes and Observations: _________________________________________________________

Bandwidth The total voltage range around the set voltage which the control will consider acceptable Acceptable voltage range defined as: Range = SV +/- 1/2 BW Notes and Observations: _________________________________________________________

Time Delay The number of seconds the control waits, from the start of an out-of-band condition, before initiating a tap change Typical values are 30 through 90 sec…. Notes and Observations: _________________________________________________________

Time Delay & Cascading Regulators SVR TD = 45 SEC SVR TD = 75 SEC 3-phase LTC transformer TD = 30 SEC SVR TD = 45 SEC SVR TD = 60 SEC SVR TD = 75 SEC Notes or Observations _______________________________________________________________ SVR TD = 45 SEC Rule 1: Each succeeding regulator in series down line from the source requires a longer time delay Rule 2: The minimum time delay from one regulator to the next in cascade is 15 seconds

Control Operating Mode Defines for the control how to respond to out-of-band conditions Options Sequential (FC 42 = 0) Time integrating (FC 42 = 1) Voltage averaging (FC 42 = 2) Notes and Observations: _________________________________________________________

SEQUENTIAL c=30 c=0 c=10 c=0 2 sec delays (horizontal) 30 sec. out- of-band 121.0 UBE in-band 120.0 SV time 119.0 LBE tap changes (vertical) 10 sec. out- of-band 5 sec . in-band counter resets to zero Given: SV=120.0 BW=2.0 TD=30

TIME INTEGRATING 2 sec delays (horizontal) c=30 c=0 c=10 c=4.5 out-of-band UBE 121.0 in-band 120.0 SV time LBE 119.0 tap changes (vertical) 10 sec. out- of-band 5 sec. in-band; counter decremented 1.1/sec in-band Given: SV=120.0 BW=2.0 TD=30

VOLTAGE AVERAGING average voltage tap changes w/no 2 sec. delay between taps c=30 c=0 out-of band 121.0 UBE in-band SV 120.0 time LBE 119.0 10 sec. out- of-band 5 sec. in-band Given: SV=120.0 BW=2.0 TD=30

Reverse Sensing Mode Reverse sensing mode defines for control what RPF (Reverse Power Flow) is and how it is to react Options are locked forward, locked reverse, reverse idle, bi-directional, neutral idle, and co-generation Notes and Observations: _________________________________________________________

Configuration Defines for the control how the regulator is connected in the power system Necessary for proper phase relationships Configuration = FC 41 Options Wye (FC 41 = 0) Delta lag (FC 41 = 1) Delta lead (FC 41 = 2) Notes and Observations: _________________________________________________________

System Line Voltage The nominal system voltage at which the regulator is to operate System line voltage = FC 43 Obtain value from regulator nameplate Notes and Observations: _________________________________________________________

Overall P.T. Ratio Ratio of system line voltage to voltage sensed by the control when in neutral position Overall PT ratio = FC 44 Obtain value from nameplate based on selected system line voltage Notes and Observations: _________________________________________________________

Nameplate System Voltages 14400 Volts, 60 Hz TAP CONTROL INTERNAL R.C.T. TEST OVERALL IN LOAD WDG.TAP P.T. TAP TERMINAL POT. USE VOLTS (TANK) RATIO (CONTROL) VOLTAGE RATIO 14400 E1 120:1 120 120 120:1 13800 E1 120:1 115 120 115:1 13200 E1 120:1 110 120 110:1 Notes and Observations: _________________________________________________________ 12000 E1 120:1 104 115 104:1 7970 E2 60:1 133 120 66.5:1 7620 E2 60:1 127 120 63.5:1 7200 E2 60:1 120 120 60:1 6900 E2 60:1 115 120 57.5:1 Note: The ratios may be different for each load current rating

Line Drop Compensation VDROP L S I R X FC 9 SL VCOMP VIN Load Center VOUT FC 7 FC 8 FC 6 Notes and Observations: _________________________________________________________ VCOMP = VOUT - VDROP R VR FC 4 X VX FC 5