GB2267399A

GB2267399A - Controlling the output voltage of a power transformer

Info

Publication number: GB2267399A
Application number: GB9211234A
Authority: GB
Inventors: Nicholas John Hiscock; Christopher Robin Goodfellow
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-05-27
Filing date: 1992-05-27
Publication date: 1993-12-01
Anticipated expiration: 2012-05-27
Also published as: GB2267399B; GB9211234D0

Abstract

A monitoring system prevents the voltage applied to an electrical distribution network reaching unacceptable levels if a voltage control system in use to initiate the operation of regulating tap change equipment attached to a power transformer is wrongly set or fails in such a way that the voltage level would be taken outside acceptable limits. Output voltage 100 from a tap change regulated transformer is connected to each of four comparators 1, 2, 3, 4, which also receive successively higher reference voltages from a source 101. Comparators 2, 3 are connected to relays 102, 103 which inhibit any further lowering or raising tap change operations if voltage 100 falls below or exceeds the corresponding reference voltage. Comparators 1, 4 actuate an alarm 106 if outer reference limits are reached. <IMAGE>

Description

SPECIFICATION A SCHEME TO PREVENT THE OUTPUT VOLTAGE OF POWER TRANSFORMERS FROM BEING DRIVEN OUTSIDE A PRESET LEVEL.

Large power transformers are equipped with motorised tap changing equipment which may be operated under electrical control in order to change the primary to secondary winding ratio such that a desired supply voltage can be achieved at the output terminals of the transformer for changing power system conditions.

The control circuitry for such tap changing equipment, if incorrectly operated, will allow the voltage at the output terminals of the power transformer to be set to a value which is outside the correct voltage for the circuit to which the transformer is connected.

Transducers connected to the output connections of these power transformers are used in conjunction with a voltage sensing system having settings arranged to operate the tap change mechanism in such a way that the output voltage is maintained between upper and lower limits.

If the voltage is between these upper and lower limits, no tap changing operations are initiated by the sensing relay.

If the voltage falls towards the lower band of the sensing relay then a raise tap change operation is to be expected. If the voltage rises towards the upper band of the sensing relay then a lower tap change operation is to be expected. If the voltage exceeds either limit for a time that is greater than the tap changer operating time necessary to return the voltage within the sensing relay limits, an unacceptable power system condition will exist.

The invention is a device, which may be self contained or provided as a module within another system, which monitors the transformer output voltage level and operates a control device, the output from which may be used to inhibit further operations of the tap changing mechanism if the voltage moves outside preset limits which are set to be within the sensing relay upper and lower limits, and also a timed alarm device, the output of which may be used to send a remote warning signal if the voltage moves outside preset limits which are set to be just outside the sensing relay upper and lower limit settings.

DESCRIPTION A specific embodiment of the invention is now described by way of example with reference to figure 1 and describes an arrangement in use with a tap changing mechanism used with a power transformer.

An output signal 100, usually a voltage derived from voltage transformer connected to the output terminals of a power transformer, is applied to one input on each of 4 electronic comparators 1,2,3 & 4, the other inputs to which are provided with a proportion of a reference voltage 101 by a number of resistors 10,11,12,13,14 are connected in series to this reference voltage such that each comparator receives a different level of reference voltage at its other input and that the voltage is lowest at the input to 1 and highest at the input to 4.

When the input from 100 is at a level that is greater than the level at point 11/12 and less than at point 12/13, no outputs are provide by comparators 1,2,3 or 4.

When the input from 100 is at a level that is greater than the level at point 10/11 and less than at point 11/12, an output is provided by comparator 2 which operates a relay 102, the output contacts 105 of which are connected into the control circuitry of the tap change mechanism such as to prevent any further operations which would lower the voltage at the output terminals of the power transformer.

When the input from 100 is at a level that is less than the level at 10/11, an output is provided by comparator 1 and 2.

When the input from 100 is at a level that is greater than the level at point 12/13 and less than at point 13/14, an output is provided by comparator 3, which operates a relay 103, the output contacts 104 of which are connected into the control circuitry of the tap change mechanism such as to prevent any further operations which would raise the voltage at the output terminals of the power transformer.

When the input from 100 is at a level that is greater than the level at point 13/14 an output is provided by comparator 3 and 4.

The outputs from comparators 1 and 4 are connected to operate an alarm mechanism 106, the output contacts of which are used to remotely indicate an unacceptable voltage level at the output terminals of the power transformer as detected at 100.

Claims

A device comprising electrical circuitry which receives a signal that is proportional to the voltage measured at the output terminals of a power transformer, the signal being applied to a series of comparators, the output of the first comparator being arranged to operate relay contacts or the like if the output voltage falls below a preset value, the second comparator is set to operate at a level above the first comparator such that the difference allows for the level that the voltage at the output terminals of the power transformer can reach before a corrective action is initiated by the control system and being arranged to operate relay contacts or the like which may be used to inhibit operations of a tap changing mechanism to reduce the output voltage, the third comparator is set to operate at a level below the fourth comparator such that the difference allows for the level that the voltage at the output terminals of the power transformer can reach before a corrective action is initiated by the control system and being arranged to operate relay contacts or the like which may be used to inhibit operations of a tap changing mechanism to increase the output voltage and the fourth comparator being arranged to operated relay contacts or the like if the output voltage is greater than a preset value.