GB2190219A

GB2190219A - Voltage control for high voltage power transformers

Info

Publication number: GB2190219A
Application number: GB08610881A
Authority: GB
Inventors: Nicholas John Hiscock; Christopher Robin Goodfellow
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-05-03
Filing date: 1986-05-03
Publication date: 1987-11-11
Anticipated expiration: 2006-05-03
Also published as: GB8610881D0; GB2190219B

Abstract

In a system in which a plurality of power transformers supply a common load busbar and each transformer has a respective tap- charging voltage regulator, control signals for the regulators are derived by a circuit in which currents representing the power transformer load currents pass through interposing transformers T1 to be summed by a buswire B, the summed current then passing through interposing transformers T2 via link X, Y and buswire A. The voltage produced across each line drop compensation resistor LDC is proportional to the total load regardless of the number of power transformers in service and does not contain components of circulating current, Any circulating current component present in transformer T1 affects the phase and amplitude of the voltage produced by inductors, INDUCTANCE, in the regulator circuits, each inductor being connected in such a way that this voltage offsets the tendency for the regulator to initiate a tap change which would increase the circulating current. The illustrated circuit is used where the regulator circuit has a norminal 30 (or 210) degree relation between voltage and current, modifications for use where a nominal 90 (or 270) degree relation exists include provision of a variable inductor as the LDC element. <IMAGE>

Description

SPECIFICATION A voltage control scheme for high voltage power transformers This invention relates to a device that is applied to new or existing voltage regulator circuits as used with High Voltage Power Transformers.

For clarity, a number of terms used within the text have the meanings as follows: ON LOAD TAP CHANGER: A device attached to a power transformer which changes the winding/winding turns ratio and thereby varies the output voltage.

LINE DROP COMPENSATION (LDC): The increase in the supply voltage of a circuit such that the drop in voltage due to load at the far end of the circuit is minimised.

FIRM CAPACITY: The electrical load which can be supplied from a particular location after allowance is made for the loss of items of plant.

COUPLING CHARACTERISTIC: A voltage produced within the invention which is applied to the voltage regulating circuitry.

CIRCULATING CURRENT: The current which flows between interconnected transformers as a result of the difference in their open-circuit voltages.

There are problems with existing tap change schemes as follows: 1. Many schemes suffer from the disadvantage that, following the automatic disconnection of one transformer on fault, either the voltage control is lost completely, or the line drop compensation setting is increased above the required value.

2. Many existing tap change schemes must be made inoperative before paralleling substations.

3. Many tap change control circuits are very complex and rely on the satisfactory operation of numerous electrical contacts.

This invention, has been developed for voltage control systems. It possesses the following features: 1. Voltage control and line drop compensation is maintained regardless of the number of transformers in service.

2. No necessity to render voltage control inoperative when paralleling between sub stations.

3. The LDC and coupling characteristic down to low power factors is satisfactory.

4. Suitable for use in 1, 2, 3 or 4 transformer locations.

5. Inherently simple and reliable with few components.

6. Enables transformers having incompatible tap change equipment to run in parallel.

7. Can be applied to 30, 90, 210, or 270 degree connected schemes.

The Scheme provides for the interconnection of current transformer outputs in multitransformer substations such that the load current component of each power transformer is summated, converted to a common base and applied to each voltage regulating device for the purpose of line drop compensation.

The circulating current component of each power transformer is caused to apply a corrective voltage to its own regulating device.

An inductance provides a reverse reactance characteristic in voltage regulating circuits having a 30 degree (or 210 degree) vector difference between the reference voltage and the current transformer used for this application.

The invention consists of 3 basic components, 2 transformers and an inductance. Connections are made into the voltage regulator circuitry and inter-connections made between modules. The unit is compact and can easily be accommodated in the majority of existing tap change control panels.

Taking a location with two transformers as a specific example, the invention is used and functions as follows: Figure 1 shows the invention connected for operation at a location where the two Power transformers supply load to a common busbar. The voltage and current connections are such that there is a nominal 30 degree (or 210 degree) relationship.

Consider the normal operation of the circuit.

The secondary current from each power transformer passes through the respective T1 interposing transformers before being summated by buswire B, connected between the modules. The summated current now passes through each of the T2 interposing transformers in turn via link X on the second module, buswire A and link Y on the first module.

Connections are provided on the T2 interposing transformers such that the secondary output is correct for the substation firm capacity.

The voltage produced across each LDC resistor is proportional to the total substation load, regardless of the number of power transformers in service, and does not contain components of circulating current. This has the advantage that the LDC setting need not be adjusted, regardless of the number of transformers in service.

Any component of circulating current present in the T1 interposing transformers, affects the physical angle and to some extent the magnitude of, the voltage produced by the inductance used in the regulator circuit. The required value of inductance is selected by link Z. The inductance is connected in such a way that this voltage offsets the tendency for the regulating relay to initiate a tapchange which will increase the circulating current.

The invention can be applied to a voltage regulating circuit having a nominal 90 degree (or 270 degree) relationship between the voltage and current. In order to provide the required vector quantities the LDC control is a variable inductance and the coupling characteristic is produced by a resistance.

Claims

1. A voltage control scheme for High Voltage power transformers which provides for the interconnection of current transformer outputs in multi-transformer substations such that the load current component of each power transformer is summated, converted to a common base and applied to each voltage regulating device for the purpose of line drop compensation.

An inductance provides a reverse reactance characteristic in voltage regulating circuits with a nominal 30 degree (or 210 degree) relationship between the voltage and current.

2. A voltage control scheme for High Voltage power transformers as claimed in claim 1. wherein a resistance provides a reverse reactance characteristic in voltage regulating circuits with a nominal 90 degree (or 270 degree) relationship between voltage and current.