EENG 105: Voltage Regulators & AVRs

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Questions and Answers

A complete time-delay is required before another tap change can take place during the ______ operating mode.

control

The time-delay circuit is activated when the load voltage goes ______ of band.

out

The timer is reset when the voltage stays in-band for at least ______ continuous seconds.

10

In the time integrating mode, the timer is decremented at the rate of ______ seconds for every second elapsed.

<p>1.1</p> Signup and view all the answers

When power flows in the normal direction, the PT is connected across the ______ side of the AVR.

<p>load</p> Signup and view all the answers

AVRs will raise the loading capability on the output side but not on the ______ side.

<p>input</p> Signup and view all the answers

The primary side of the power transformer bank is one of the typical AVR ______.

<p>locations</p> Signup and view all the answers

The step voltage regulator principle includes a basic ______.

<p>transformer</p> Signup and view all the answers

A step-up autotransformer increases voltage while a step-down ______ decreases it.

<p>autotransformer</p> Signup and view all the answers

In reverse power flow, the relationship between T2 and V2 causes changes in V1 and ______.

<p>T1</p> Signup and view all the answers

Older types of AVR control required an optional Reverse Power Flow ______ kit.

<p>Detector</p> Signup and view all the answers

The sequence of regulator tap-changer operation can have different ______ states.

<p>operation</p> Signup and view all the answers

If V2 is low, the control signals the AVR to raise the voltage by increasing ______.

<p>T2</p> Signup and view all the answers

A step voltage regulator can show its two fingers for ______-changing.

<p>tap</p> Signup and view all the answers

The regulator control theory involves a tap-changing ______ for operation.

<p>motor</p> Signup and view all the answers

The equation that governs the relationships in power flow is V1 T1 = V2 ______.

<p>T2</p> Signup and view all the answers

Newer AVR controls now have reverse sensing modes as a ______ feature.

<p>standard</p> Signup and view all the answers

The line drop compensator is part of the ______ circuit in voltage regulation.

<p>control</p> Signup and view all the answers

The common reverse sensing mode that ensures normal power flow includes Locked Forward and Locked ______.

<p>Reverse</p> Signup and view all the answers

The customer tapping point is one of the key ______ in the voltage regulation process.

<p>locations</p> Signup and view all the answers

In the case of reverse power flow, if T1 remains constant, V1 or the new load side ______ must decrease.

<p>voltage</p> Signup and view all the answers

AVRs are crucial for maintaining voltage stability in the ______ network.

<p>electrical</p> Signup and view all the answers

The turns ratio is an important factor in determining how voltage at Source A and ______ relate to each other.

<p>Source B</p> Signup and view all the answers

The ______ supplies a signal to the control proportional to the line voltage.

<p>PT</p> Signup and view all the answers

The signal from the PT is modified by the line-drop ______ settings.

<p>compensator</p> Signup and view all the answers

The voltage ______ signals when the voltage goes out of a preset band.

<p>sensor</p> Signup and view all the answers

After the voltage has been out of the bandwidth for a preset ______, a signal is sent to the tap-changing motor.

<p>time</p> Signup and view all the answers

The tap-changing motor will continue to change ______, correcting the voltage on the line.

<p>taps</p> Signup and view all the answers

The sensed voltage must be within the preset ______ for normal operation.

<p>bandwidth</p> Signup and view all the answers

The major components of an ______ include the PT, compensator, and tap changer.

<p>AVR</p> Signup and view all the answers

The ______ changing motor operates to correct the voltage when it is outside the specified range.

<p>tap</p> Signup and view all the answers

Voltage Limiting is used to place both a high and low limit on the output ______ of the regulator.

<p>voltage</p> Signup and view all the answers

Voltage Reduction allows the regulator to reduce voltage during situations where power demands surpass the available ______.

<p>capacity</p> Signup and view all the answers

The Automatic Load Bonus feature limits the range of regulation when a fixed ______ level is reached.

<p>current</p> Signup and view all the answers

Harmonic Measurement can include various orders such as 3, 5, 7, 9, and ______ harmonic for CL-5A.

<p>13th</p> Signup and view all the answers

The ADD-AMP feature in Cooper AVRs allows the operation of the AVR at higher than nameplate ______.

<p>currents</p> Signup and view all the answers

By-passing a regulator off neutral will ______-circuit the series winding left energized.

<p>short</p> Signup and view all the answers

Do not depress the drag hand reset button for more than ______ seconds.

<p>5</p> Signup and view all the answers

Lightning protection is connected from line to ______.

<p>ground</p> Signup and view all the answers

The voltage level for both GE's VR-1 and SM-3 models ranges from ______ to 135.

<p>105</p> Signup and view all the answers

The time delay for the GE SM-3 model is between 10 and ______ seconds.

<p>180</p> Signup and view all the answers

The band-edge indicator in GE's AVR controls is an ______ for the VR-1 model.

<p>LED</p> Signup and view all the answers

The Siemens Type JFR step voltage regulator has a power rating of ______ kVA in one of its configurations.

<p>250</p> Signup and view all the answers

For the Siemens MJ-3A control, the voltage bandwidth is ______.

<p>1-6</p> Signup and view all the answers

Both the GE and Siemens AVR controls feature a ______ indicating light.

<p>Neutral</p> Signup and view all the answers

The operations counter for the Siemens MJ-XL control is ______.

<p>Electronic</p> Signup and view all the answers

In GE's AVR controls, the data port is available for the SM-3 but ______ for the VR-1.

<p>not available</p> Signup and view all the answers

The manual control switches for the Siemens MJ-XL include ______, OFF, and Auto options.

<p>Manual</p> Signup and view all the answers

Both Siemens AVR models have a motor fuse that is ______.

<p>Yes</p> Signup and view all the answers

Flashcards

Voltage Level

The voltage that is desired to be maintained in the system, typically between 119V and 121V.

Voltage Regulator

A device used to adjust the voltage in a power system, usually located at a substation.

Voltage Sensor

The part of the regulator that senses the actual voltage on the power line.

Time Delay

The time delay built into the regulator before the voltage control action begins.

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Line Drop Compensation

The ability to adjust for variations in voltage drop along the power line.

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Tap Changer

The part of the regulator that allows the voltage to be adjusted by changing the turns on the transformer.

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Tap Changing Motor

The motor used to physically change the taps on the transformer, altering the voltage.

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Potential Transformer (PT)

The part of the regulator that supplies the signal to the control system based on the line voltage.

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Time Delay Feature

The time delay feature prevents rapid tap changes, ensuring stability in the system. It allows for a delay before a new tap change can occur.

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Voltage Averaging Mode

This mode aims to stabilize the voltage by averaging instantaneous readings and adjusting the tap accordingly. It helps to mitigate voltage fluctuations by taking a smoother approach.

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Timer Reset Condition

In this mode, the system waits for the voltage to stay within the acceptable range for a period of 10 continuous seconds before resetting the timer. This avoids unnecessary tap adjustments caused by momentary voltage shifts.

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Time Integrating Mode

A technique used in voltage regulation to ensure a smooth transition between tap adjustments. Instead of immediate changes, it gradually reduces the timer at a rate of 1.1 seconds per second passed, until it reaches zero.

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Reverse Power Flow

Power flowing in the opposite direction from the intended flow, typically from the load to the source (e.g., a generator). This can be problematic for voltage regulation and may require adjustments.

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AVR Impact on Voltage

Automatic Voltage Regulators (AVRs) increase the voltage at the output of a system, but not at the input.

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Typical AVR Locations

AVRs are typically installed in various locations within an electrical system, including the primary side of a power transformer, the secondary of a power transformer, the main line of a feeder, the middle of a feeder, and at customer tapping points.

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Pole-mounted AVRs

Pole-mounted AVRs are usually found on utility poles and are generally used for smaller applications.

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Platform-mounted AVRs

Platform-mounted AVRs are often used in larger installations, such as substations, and are typically placed on a platform for easy access and maintenance.

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Step-up/Step-down Autotransformer

An autotransformer can be set up as a step-up transformer, where the output voltage is higher than the input voltage, or as a step-down transformer, where the output voltage is lower than the input voltage.

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Step Voltage Regulator

A step voltage regulator is a type of transformer that uses tap-changing to adjust the output voltage based on the load demand.

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Step voltage regulator tap-changing

Step voltage regulators use a tap changer mechanism to adjust the voltage by selecting different turns on the transformer winding.

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Reversing Switch in Step Voltage Regulators

The step voltage regulator uses a reversing switch to allow it to both raise (increase) and lower (decrease) the output voltage, providing flexibility.

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Step Voltage Regulator Tap Changing Sequence

The step voltage regulator's operation involves moving through a series of taps to adjust the output voltage according to load changes.

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Step Voltage Regulator Control Theory

A step voltage regulator monitors the voltage at the load, compares it to a setpoint, and uses line drop compensation to determine the necessary tap adjustments to maintain a stable voltage.

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Locked Reverse

A method of controlling an AVR where the voltage regulation is based on the source voltage (V2) even when power flow is reversed, but the AVR still maintains the original winding configuration.

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Locked Forward

The voltage regulation of an AVR is based on the voltage at the source winding (V1) even when power flow is reversed.

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Reverse Sensing Modes

A method where the AVR adjusts its regulation based on the power flow direction, either normal or reverse, ensuring proper operation.

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Normal Regulation

The voltage regulation of an AVR is based on the source voltage (V2) when power flow is normal (from Source A to Source B) or reversed.

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Turns Ratio

The number of turns in the primary winding (T1) and the secondary winding (T2) of a transformer dictates the voltage transformation based on the relationship: V1/V2 = T1/T2.

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AVR (Automatic Voltage Regulator)

A device that regulates the output voltage of a generator by adjusting the excitation current.

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Transformer

An electrical component that changes the voltage from one level to another based on the windings ratio.

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Voltage Bandwidth

The difference in voltage between the upper and lower voltage limits.

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LDC Resistance Volts

How much voltage drop on the line is compensated by the AVR control.

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LDC Reactance Volts

The amount of reactive power compensation that the AVR control can handle.

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Band-edge Indicator

A component that signals when the voltage is outside the permitted range.

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Manual Control Switches

A switch that allows for manual control of the AVR to adjust voltage settings.

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Switching Modes

The ability of the AVR control to change taps sequentially or all at once.

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Data Port

A port that allows for electronic communication with the AVR control.

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Supervisory ON/OFF Switch

A special feature that allows the AVR control to be turned on and off externally.

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Voltage Limiting

A feature that prevents the output voltage from going above or below a specific range, protecting connected equipment.

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Voltage Reduction

Allows the regulator to lower the output voltage when the demand for power exceeds the available supply, preventing overloading.

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Automatic Load Bonus

A feature that limits the range of voltage adjustment when a certain current level is reached, enhancing system stability.

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Load Bonus Capability

The ability of the AVR to operate at currents greater than the rated nameplate capacity when the voltage regulation range is restricted.

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Load Current Ratings

The ratio of maximum allowable current to rated current, depending on the desired regulation range.

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Series Winding Protection

A safety measure that protects the series winding from damage due to high currents.

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Lightning Protection

Protects the system from lightning strikes by diverting the current to the ground.

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Bypassing a Regulator

A procedure that removes the regulator from service by bypassing it, requiring specific precautions to avoid damaging equipment.

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Study Notes

EENG 105: Distribution System & Substation Design - Topic 5

  • Voltage Regulators: A system designed for automatic constant voltage maintenance. Designs can be simple feed-forward or include negative feedback, using electromechanical or electronic components.
  • Automatic Voltage Regulators (AVRs): Tap-changing autotransformers continuously monitor output voltage, adjusting taps for desired voltage. Voltage regulation is typically 10% raise (boost) to 10% lower (buck) in approximately 5/8 steps (32 steps total).
  • Reasons for Installing AVRs: Improve system voltage, enhance quality of service, and meet regulatory standards.
  • Effects of AVRs on Voltage Problems: Solved problems include undervoltage, overvoltage, and unbalanced voltage. Problems not solved include voltage sags, swells, and fluctuations.

AVR & Capacitor Bank Functions

  • AVR Functions:
    • Raise/lower voltage
    • Voltage adjustment on source side
    • Small voltage step control in varying switching operations with no need for frequent inspection.
    • Reduced losses throughout the system
    • Reduced thermal loading
    • Raises system loading capability
  • Capacitor Bank Functions (in conjunction with AVRs):
    • Raise/lower voltage (effect displayed by being switched on/off)
    • Switching can cause capacitor deterioration in large operations per day.
    • Reduced losses can be noticed on the output side.

Typical AVR Locations

  • Primary side of power transformer bank
  • Secondary of power transformer bank
  • Main line of feeder
  • Middle of feeder
  • Customer tapping point

Voltage Regulator Control Theory

  • Potential Transformer: Connected across load side, providing proportional voltage for control and the tap changing motor.
  • Line Drop Compensator: Reduces voltage swings, increases voltage during full load, and is connected to the potential transformer to the regulator.
  • Voltage Sensor: Compares input voltage to preset value, adjusts control to maintain the voltage level within a given tolerance.
  • Time Delay: Allows the regulator to ignore brief voltage variations or corrections but corrects for prolonged out-of-band conditions.

Voltage Regulator Operating Sequence

  • Potential Transformer (PT): Provides a signal to the control, proportional to line voltage
  • Signal Modification: Through line-drop compensator settings
  • Voltage Sensor Signal: Indicates when voltage drops out of the preset bandwidth
  • Tap-Changing Motor Activation: Initiates tap changes for voltage correction until returned to the given bandwidth

Major Components of an AVR

  • S (Source) Bushing
  • L (Load) Bushing
  • SL (Neutral) Bushing
  • Series Arrester
  • Position Indicator: Mechanical pointer for tap switch position, indicating raise/lower limits.
  • Electronic Control: Controlling component, with specific features depending on the control type.

Siemens, Cooper, & GE AVR Control Types

  • Cooper/McGraw Edison VR-32
  • Cooper CL-2/CL-2A
  • Cooper CL-4C
  • Cooper CL-5A
  • GE VR-1
  • GE SM-3

Typical Features of an Electronic Control

  • Voltage Level Selector
  • Bandwidth Selector
  • Time Delay Selector
  • Band-edge Indicator
  • Line Drop Compensation
  • Neutral Indicating Light
  • Draghand Reset/Neutral Light Test Button
  • Internal/External Power Switch
  • External Power Terminals
  • Voltmeter Terminals
  • Motor and Panel Fuses
  • Operations Counter
  • Data Port
  • LCD display
  • Keypads

Control Operating Modes

  • Sequential: One by one tap changes until reaching the target voltage
  • Non-sequential: Single tap change, then reset
  • Time Integrating: Timer counts down at a rate; once reaching zero, the timer is reset
  • Voltage Averaging: Microprocessor monitors and averages load voltage; taps change to correct; timer reset after voltage within band

Reverse Sensing Modes

  • Locked Forward: Control remains in forward direction
  • Locked Reverse: Control remains in reverse direction
  • Bi-directional: Adjusts in forward/reverse directions based on user thresholds

Regulator Connection Diagrams

  • One-phase 3-phase, and other circuit regulations
  • Different types of AVR (Wye, Delta connected types)

AVRs Used by Meralco

  • Manufacturers of AVRs used for power regulation

Voltage Drop Calculation

  • Formula for calculating voltage drop in a copper wire utilizing Length, Area, Current, and constant 0.017
  • Formula notes for appropriate use with 25°C copper

Important Reminders

  • Series winding protection is distinct from lightning protection measures, with separate wire connections.
  • Ensure the regulator is in the neutral position before bypassing to avert potential damage from mismatched impedance
  • Avoid holding the drag hand reset button for longer than 5 seconds

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