EENG 105: Distribution System & Substation Design PDF

VOLTAGE REGULATORS A Voltage Regulator is a system designed to automatically maintain a constant voltage. A Voltage Regulator may use a simple feed-forward design or may include negative feedback. it may use an electromechanical mechanism, or electronic components. VOLTAGE R...

VOLTAGE REGULATORS A Voltage Regulator is a system designed to automatically maintain a constant voltage. A Voltage Regulator may use a simple feed-forward design or may include negative feedback. it may use an electromechanical mechanism, or electronic components. VOLTAGE REGULATORS A Voltage Regulator may use a simple feed-forward design or may include negative feedback. it may use an electromechanical mechanism, or electronic components. AUTOMATIC VOLTAGE REGULATORS A tap-changing autotransformer with the ability to continuously monitor its output voltage and automatically adjust itself by changing taps until the desired voltage is obtained. It regulates line voltage from 10% raise (boost) to 10% lower (buck) in 32, approximately 5/8 steps.  Reasons for Installing AVRs To improve system voltage To improve quality of service To meet regulatory standards Effects of AVRs on Voltage Problems Problems Solved by AVRs Undervoltage Overvoltage Unbalanced voltage Problems Not Solved by AVRs Voltage sags Voltage swells Voltage flickers/fluctuations Functions Performed by AVRs & Capacitor Banks FUNCTION AVR CAP COMMENTS 1. Can raise & lower voltage Yes Yes* *Will give the effect by being switched on or off 2. Can raise voltage on source No Yes side 3. Capable of small voltage Yes No* *Will produce small changes in step control voltage if bank size is small 4. Capable of many switching Yes No* *Capacitor switch contacts operations w/o frequent deteriorate rapidly with large inspection number of switching operations per day 5. Reduces losses in the No* Yes *Some reduction in losses may system result on output side by virtue of increased voltage 6. Reduces thermal loading No Yes 7. Raises system loading Yes* Yes *AVRs will raise the loading capability capability on output side but not on input side Typical AVR Locations 1 1. Primary side of power Power transformer bank Transformer 2 2. Secondary of power Substation Bus transformer bank 3 Feeders 3. Main line of feeder 5 Core 4. Middle of feeder Customer 4 5. Customer tapping point Sample AVR Installation (Pole Mounted) Sample AVR Installations (Platform Mounted)  STEP VOLTAGE REGULATOR PRINCIPLE BASIC TRANSFORMER + + - - STEP-UP AUTOTRANSFORMER + + - - STEP-DOWN AUTOTRANSFORMER + + - -  STEP VOLTAGE REGULATOR PRINCIPLE STEP REGULATOR + + - - STEP REGULATOR Step voltage regulator + showing its 2 fingers + for tap-changing - - STEP REGULATOR Step voltage regulator with the reversing switch + that facilitates raise & lower operations - STEP VOLTAGE REGULATOR PRINCIPLE Sequence of Regulator Tap-Changer Operation 3 1 0 2 1 0 1 1 0  REGULATOR CONTROL THEORY LOAD POTENTIAL LINE DROP VOLTAGE TIME TRANSFORMER COMPENSATOR SENSOR DELAY TAP TAP CHANGING MOTOR CHANGER Step Voltage Regulator Operating Sequence  REGULATOR CONTROL THEORY 1. Potential Transformer Connected across the load side of the regulator Provides a voltage proportional to the circuit voltage for the control Provides a voltage for the tap changing motor 19.92 kV 120 V To Tap-changing Motor  REGULATOR CONTROL THEORY 2. Line Drop Compensator Functions to minimize the voltage swings at any point on the line, due to changes in load current It has the effect of increasing the voltage at the output of the regulator at full load CT POTENTIAL TRANSFORMER VOLTAGE SENSOR X R REACTANCE RESISTANCE  Line Drop Compensation Principle Point of Regulation End of Line No Load 7200V 7200V NO LINE DROP COMPENSATOR Full Load 6800V 7400V No Load 7200V 7200V WITH LINE DROP COMPENSATOR Full Load 7000V  REGULATOR CONTROL THEORY 3. Voltage Sensor It compares the input voltage to a preset value (“voltage setting”) & a tolerance in voltage allowed around the voltage level (“bandwidth”) If the voltage detected by the sensor is out of the bandwidth, the control will operate to either raise or lower the voltage output of the regulator until the voltage fed back to into the sensor is again within the bandwidth. 121V BANDWIDTH 120V Voltage Level 119V  REGULATOR CONTROL THEORY 4. Time Delay Permits the regulator to ignore brief, self-correcting voltage variations. Enables the regulator to correct only those voltage variations which exist for longer than a preset time. 121V Voltage Level 120V 119V ~ ~  Voltage Regulator Operating Sequence PARTS OF CONTROL LOAD The PT supplies a signal to the POTENTIAL LINE DROP VOLTAGE TIME control proportional to the TRANSFORMER COMPENSATOR SENSOR DELAY line voltage The signal is modified by the line-drop compensator settings TAP TAP The voltage sensor signals CHANGING CHANGER MOTOR when the voltage goes out of a preset band  Voltage Regulator Operating Sequence After the voltage has been PARTS OF CONTROL LOAD out of the bandwidth for the preset time, a signal is POTENTIAL LINE DROP VOLTAGE TIME sent to the tap-changing TRANSFORMER COMPENSATOR SENSOR DELAY motor to operate to correct the voltage The tap-changing motor will continue to change TAP TAP taps, correcting the CHANGER CHANGING MOTOR voltage on the line, until the sensed voltage is again within the bandwidth  4 1 2 3 MAJOR COMPONENTS OF AN AVR 5 1. S (Source) Bushing 2. L (Load) Bushing 3. SL (Neutral) Bushing 4. Series Arrester 6 5. Position Indicator 6. Electronic Control MAJOR COMPONENTS OF AN AVR Position Indicator Has a pointer mechanically connected to the tap-changing switch Indicates the actual position of the tap- changer through the yellow pointer Indicates the maximum & minimum positions attained during raise & lower operations through its drag hands. Allows load bonus setting of the regulator MAJOR COMPONENTS OF AN AVR Series Arrester A bypass arrester connected across the series winding between the S & L bushings. Limits the voltage developed across the series winding during lightning strikes, switching surges & line faults. Typical Features of an Electronic Control 1. Voltage Level Selector 2. Bandwidth Selector 3. Time Delay Selector 4. Band-edge Indicator 5. Line Drop Compensation Selectors 6. Neutral Indicating Light 7. Draghand Reset/Neutral Light Test Button 8. Internal/External Power Switch  Typical Features of an Electronic Control 9. Control Switch 10. External Power Terminals 11. Voltmeter Terminal 12. Motor & Panel Fuses 13. Operations Counter 14. Data Port 15. LCD Display 16. Keypads  Typical Features of an Electronic Control For older controls like the CL-2, VR-1 & MJ-3A the following 3 features are set through rotary switches. For microprocessor types, these features are accessed through keypads 1. Voltage Setting or Set Voltage The voltage level to which the control will regulate, on the 120-volt base. 2. Bandwidth Total range around the voltage setting, which the control will consider as satisfied condition 3. Time delay Period of time (in seconds) that the control waits before initiating a tap-adjustment  Typical Features of an Electronic Control 4. Band-edge Indicators Indicate LOW or HIGH out-of-band condition of the voltage 5. Line Drop Compensation Selectors Used for individual settings of the resistance and reactance drop compensation 6. Neutral Indicating Light (Neutralite) Primary indication that the tap-changer is in the neutral position 7. Draghand Reset/Neutral Light Test Switch Moves the draghands to the present position of the main/yellow hand. Also tests the neutral light in some controls.  Typical Features of an Electronic Control 8. Internal/external Power Switch In the Internal position, the control & tap-changer motor gets power from the regulator. In the External position power comes from an external AC source. In the OFF position, no power is delivered to either the control & the motor. 9. Control Switch For setting the AVR in Manual or Automatic mode. In older controls, the same switch is used for manually raising and lowering the tap-changer  Typical Features of an Electronic Control 10. External Power Terminals Connecting 120-volt AC to these terminal powers the control & the tap-changer motor during tests or maintenance. 11. Voltmeter Terminals Allows measurement of the voltage sensed by the control (load side). 12. Motor & Panel Fuses Protects the tap-changer motor & the control panel circuit 13. Operations Counter Records the tap change operations of the AVR.  Typical Features of an Electronic Control These 3 features are found only in microprocessor-based controls like Copper’s CL-4C and CL-5A and GE’s SM-3. 14. Data Port For temporary connection with a PC during control programming & data downloading. 15. LCD Display Displays control settings, metering values & annunciator words. 16. Keypads Used in conjunction with the LCD Display for local control programming & navigation.  Control Operating Modes The manner in which the control responds to out-of-band conditions. 1. Sequential 2. Non-sequential 3. Time Integrating 4. Voltage Averaging  Control Operating Modes 1. Sequential When the load voltage goes out of band, the time-delay circuit is activated. At the end of the time-out, a tap change is initiated. After each tap change a a short pause (2 sec for Cooper controls) occurs to permit the control to sample the voltage again. Any time the voltage goes in-band, the timer is reset. This is the default setting for Cooper AVRs 2. Non-sequential Only one tap change takes place, then the time-delay is reset. A complete time-delay is required before another tap change can take place.  Control Operating Modes 3. Voltage Averaging When the load voltage goes out of band, the time-delay circuit is activated. During this time the microprocessor monitors & averages the instantaneous load voltage. It then computes the number of tap changes required to bring the average voltage back to the set voltage. When the time-delay period is complete, the computed number of taps is performed without delay between them, up to a maximum of 5 consecutive tap changes. The timer is reset when the voltage stays in- band for at least 10 continuous seconds.  Control Operating Modes 4. Time Integrating Operates like the sequential mode, except that when the voltage goes in-band, the timer is not immediately reset. The timer is decremented at the rate of 1.1 seconds for every second elapsed, until it reaches zero.  REVERSE POWER FLOW When power flows in the normal direction, the PT is connected across the load side of the AVR & measures its voltage output. With the output from the AVR (V2) low, the PT senses the low voltage, & the control operates to put more series winding into the circuit. Thus the output voltage (V2) would increase & correct the situation. Reverse Power Series Flow Normal Power Winding Flow L Turns Ratio S PT Source B Equation T2 V1 T1 Source A V1 T1 V2 -- = -- V2 T2 SL To Control  REVERSE POWER FLOW Reverse Power Series Flow Normal Power Winding Flow L Turns Ratio PT Source B S Equation T2 Source A V2 V1 T1 V1 T1 -- = -- V2 T2 SL If the AVR is connected for normal regulation from Source A but is fed from Source B, the following happens: If V2 is low, the control signals the AVR to raise the voltage by increasing T2. The change in the relationship between T2 & V2 causes V1 & T1 to change to balance the equation. Since T1 will remain constant because it is the exciting winding, V1 or the new load side voltage must decrease.  Reverse Sensing Modes To ensure correct operation when the power flow reverses, older types of AVR control were provided with an optional Reverse Power Flow Detector kit. Newer AVR controls now have this as standard feature. However, several reverse sensing modes are employed, the most common of which are: 1. Locked Forward 2. Locked Reverse 3. Bi-directional  Reverse Sensing Modes 1. Locked Forward Control always operates in the forward direction. Idles in the last tap position held when more than 2% reverse current is detected 2. Locked Reverse Control always operates in the reverse direction using the reverse settings. Idles on the last tap position held when more than 2% forward current is detected.  Reverse Sensing Modes 3. Bi-directional Operates in the forward direction whenever the real component of the current is above the user defined forward threshold. 4. Operates in the reverse direction, whenever the current is above the user defined reverse threshold.  Regulator Connection Diagrams B C N 100% 110% A 10% A’ Regulating a One Phase of a 3-Phase, 4-Wire Circuit  Regulator Connection Diagrams B’ C’ B C N Regulating a 3-Phase, 4-Wire 110% 100% Circuit With 3 Regulators A 10% (Wye Connection) A’  Regulator Connection Diagrams B C VCA = 100% A C’ A’ V’CA = 110% 5% 5% Regulating a 3-Phase, 3-Wire Circuit With 2 Regulators (Open-Delta Connection)  Regulator Connection Diagrams A’ A 10% Regulating a 3-Phase, 3-Wire C VBC=100% B Circuit With 3 Regulators (Delta C’ Connection) B’ AVRs Used by MERALCO The Cooper/McGraw Edison VR-32 Step- Voltage Regulator CONTROL TYPES 1. CL-2 / CL-2A 2. CL-4C 3. CL-5A  Features of Cooper’s AVR Controls CL-2 CL-4C CL-5A Voltage Level 105-135 100-135 100-135 Rotary Switch Keypad Keypad Voltage Bandwidth 1-4.5 1-6 1-6 Rotary Switch Keypad Keypad Time Delay (Seconds) 10-120 5-180 5-180 Rotary Switch Keypad Keypad LDC Resistance Volts 0-24 ±24 ±24 Rotary Switch Keypad Keypad LDC Reactance Volts 0-20 ±24 ±24 Rotary Switch Keypad Keypad Band-edge Indicator LED LCD LCD Neutral Indicating Light Yes Yes Yes Manual Control Switches Lower-OFF-Auto-OFF-Raise Auto/Remote-OFF-Manual Auto/Remote-OFF-Manual Raise-Lower Raise-Lower Motor Fuse Yes Yes Yes Panel Fuse Yes Yes Yes Internal/External Power Switch Yes Yes Yes Operations Counter Mechanical Electronic Electronic Drag Hand Rest & Neutral Light Test Button Yes Yes Yes External Power Terminals Yes Yes Yes Voltmeter Terminals Yes Yes Yes Data Port No Yes Yes LCD Display No Yes Yes Keypads No Yes Yes Differential Voltage Fuse No Yes Yes Supervisory ON/OFF Switch No No Yes Switching Modes Sequential Sequential Sequential Non-sequential Voltage Averaging Voltage Averaging Voltage Averaging Time Integrating Time Integrating Cooper AVR with a CL-2A Control  Cooper AVR with a CL-4C Control 1 LCD Display 2 Keypad 3 Data Port 4 Power Switch 5 Voltmeter Terminals 6 External Power Terminals 7 Panel Fuse 8 Differential Voltage Fuse 9 Motor Fuse 10 Manual RAISE- LOWER Switch 11 AUTO/REMOTE-OFF- MANUAL Switch 12 Neutral Lamp Test- Drag Hand Reset Switch Input Voltage: 13 Neutral Indicating Light 80 - 170 V 45 - 65 Hz  Cooper AVR with a CL-5A Control Input Voltage: 80 - 137 V 45 - 65 Hz Cooper AVR Bank with a CL-5E Control Nameplate of a Cooper VR-32 AVR The GE Type VR-1 Step-Voltage Regulator CONTROL TYPES 1. VR-1 2. SM-3 Features of GE’s AVR Controls VR-1 SM-3 Voltage Level 105-135 105-135 Rotary Switch Keypad Voltage Bandwidth 1.5-3 1-6 Rotary Switch Keypad Time Delay (Seconds) 10-90 10-180 Rotary Switch Keypad LDC Resistance Volts ± ±24 Rotary Switch Keypad LDC Reactance Volts ± ±24 Rotary Switch Keypad Band-edge Indicator LED LCD Neutral Indicating Light Yes Yes Manual Control Switches Auto-Test-Lower-Raise-OFF Auto-Manual Raise-OFF-Lower Motor Fuse Yes Yes Panel Fuse Yes Yes Internal/External Power Switch Yes Yes Operations Counter Mechanical Electronic Drag Hand Rest & Neutral Light Test Button Yes Yes External Power Terminals Yes Yes Voltmeter Terminals Yes Yes Data Port No Yes LCD Display No Yes* Keypads No Yes Differential Voltage Fuse No No Supervisory ON/OFF Switch No Yes* Switching Modes Sequential Sequential Non-sequential Non-sequential The Siemens Type JFR Step- Voltage Regulator A 250 kVA, 7.62 kV Type JFR AVR with an MJ-3A control The Siemens Type JFR Step- Voltage Regulator A 400 kVA, 19.92 kV Type JFR AVR with an MJ-XL control Nameplate of a Siemens Type JFR AVR  Features of Siemens’ AVR Controls MJ-3A MJ-XL Voltage Level 106-134 Rotary Switch Keypad Voltage Bandwidth 1-6 Rotary Switch Keypad Time Delay (Seconds) 10-150 Rotary Switch Keypad LDC Resistance Volts ±24 Rotary Switch Keypad LDC Reactance Volts ±24 Rotary Switch Keypad Band-edge Indicator LED LED Neutral Indicating Light Yes* Yes* Manual Control Switches Manual-OFF-Auto Manual-OFF-Auto Tap Raise-Tap Lower Tap Raise-Tap Lower Motor Fuse Yes Yes Panel Fuse Yes Yes Internal/External Power Switch Yes* Yes* Operations Counter Mechanical Electronic Drag Hand Rest & Neutral Light Test Button Yes* Yes External Power Terminals Yes Yes Voltmeter Terminals Yes Yes Data Port No Yes LCD Display No No** Keypads No Yes Differential Voltage Fuse No No Supervisory ON/OFF Switch No Yes** Switching Modes  Special Features of AVR Controls 1. Voltage Limiting / First House Protector Used to place both a high and low limit on the output voltage of the regulator. 2. Voltage Reduction Allows the regulator to reduce voltage during situations where power demands surpass the available capacity, & where there are extraordinary peak loads.  Special Features of AVR Controls 3. Automatic Load Bonus Available in GE’s SM-3 control Limits the range of regulation when a fixed current level is reached in both forward and reverse operation. 4. Harmonic Measurement 3, 5, 7, 9, 11th harmonic & THD for CL-4C 3, 5, 7, 9, 11, 13th harmonic & THD for CL-5A 1-31st harmonic & THD for SM-3  LOAD BONUS CAPABILITY Allows the operation of the AVR at higher than nameplate currents when the range of regulation is restricted Called ADD-AMP feature in Cooper AVRs and VARI-AMP feature in GE & Siemens AVRs % Rated Maximum Loading Regulation 100 10 % 110 8.75 % 120 7.5 % 135 6.25 % 160 5.0 %  Effect Of Load Bonus Setting On AVR Capacity LOAD CURRENT RATINGS (IN AMPS) RATED RATED AT SPECIFIED REGULATION RANGE KV KVA ±10% ±8.75% ±7.5% ±6.25 ±5% 19.92 833 416 460 502 564 668 19.92 400 200 220 240 270 320 13.8 276 200 220 240 270 320 7.62 250 328 361 394 443 525 5 100 200 220 240 270 320  IMPORTANT REMINDERS! Series winding protection is different from lightning protection. It is connected in the line around the series winding. Lightning protection is connected from line to ground. Always make sure that the regulator is in neutral before by-passing. By-passing a regulator off neutral will short-circuit the series winding left energized. By- passing a regulator at minimum raise of lower position will result in maximum fault current because of the least impedance of the shorted series winding. Do not depress the drag hand reset button for more than 5 seconds. Holding the button for a longer period can damage the solenoid in the position indicator. VOLTAGE DROP CALCULATION To calculate voltage drop in a copper wire, use the following formula: Volts= Length x Current x 0.017 Area Volts= Voltage drop. Length= Total Length of wire in meters (including any earth return wire). Current= Current (amps) through wire. Area= Cross sectional area of copper in square millimeters. VOLTAGE DROP CALCULATION Notes This formula only applies to copper at 25°C, voltage drop increases with wire temperature, at approx 0.4% per °C. 0.017- This figure only applies to copper. Area is in square millimetres of copper, there can be confusion on how cable size is rated, with some manufacturers stating wire diameter rather than area, some even including the insulation. An explanation of this can be seen at here. VOLTAGE DROP CALCULATION Notes This formula only applies to copper at 25°C, voltage drop increases with wire temperature, at approx 0.4% per °C. 0.017- This figure only applies to copper. Area is in square millimetres of copper, there can be confusion on how cable size is rated, with some manufacturers stating wire diameter rather than area, some even including the insulation. An explanation of this can be seen at here. VOLTAGE DROP CALCULATION Example A trailer has 50M of 4 square mm wire so, how much voltage drop at 20A? 50 x 20 x 0.017= 17. Divide this by 4 (cross section area of wire): 17/4= 4.25V. In this example, the drop is 4.25V. This would mean that if there was 12V at the front of the trailer, there would only be 7.75V at the back - the lights would be very dim. This is when the wire temp is 25ºC, if the wire temp was 35ºC there would be a 4.42V drop, meaning only 7.37V at the back of the trailer. Don't forget that the current through the wire will heat it up,so even if it is only a 25ºC day, the wire will be hotter, which will increase the voltage drop. This will keep increasing until the cooling effect of the surrounding air on the wire balances the heating effect of the current. This demonstrates why it is important not to skimp on wire size when wiring a trailer. THANK YOU AND GODBLESS EE LANG MALAKAS!