Remote protection of three phase distribution transformers

A method of remotely protecting three phase electricity supply distribution transformers, comprising the steps of monitoring parameters of the supply on a distributor cable to the transformers to detect increases in transient D.C. current flowing in the respective phases, and also to detect increases in other selected functions of said parameters for identifying and quantifying a fault current flowing in the distributor cable, analysing increases in said other selected functions to identify whether said increases indicate a fault current and to quantify any such fault current and initiating the triggering of a circuit breaker to isolate the supply cable on identifying a fault current, where said circuit breaker is not triggered for any increases in said other selected functions for as long as there is a detected increase in D.C. current in any phase.

A method of remotely protecting three phase electricity supply distribution transformers, comprising the steps of monitoring parameters of the supply on a distribution cable to the transformers to detect increases in positive sequence current and to detect increases in negative sequence current resulting from unbalanced disturbance on the cable, and initiating the triggering of a circuit breaker to isolate the supply cable in response to a detected increase in negative sequence current only if there is a simultaneous detected increase in the positive sequence current in excess of a respective threshold increase.

A method of remotely protecting three phase electricity supply distribution transformers, including the steps of measuring parameters of the supply on a distributor cable to the transformers to provide time related values for the positive sequence current, voltage and phase angle, calculating therefore time related values for the susceptance of the distributor cable and load connected thereto, monitoring said time related susceptance values to detect increases in negative susceptance, and initiating the triggering of a circuit breaker to isolate the supply cable if said increase exceeds a predetermined threshold increase.

Apparatus for remotely protecting a three phase electricity supply distribution transformers, comprising means for monitoring parameters of the supply in a distributor cable to the transformers;

• control means responsive to the monitored parameters to detect an increase in at least one selected function of said parameters which can be indicative of a fault current flowing in the distributor cable, to analyse any such increase to determine the likely existance and magnitude of any such fault current, and to generate a trip signal in accordance with said analysis;
• and circuit breaker means responsive to said trip signal to isolate the supply cable;
• wherein said control means is operative to detect increases in the two functions, negative sequence current and positive sequence current, and to analyse these by comparing detected simultaneous increases in negative and positive sequence current and not initiating generation of said trip signal unless the detected negative sequence current increase exceeds a predetermined proportion of any detected simultaneous positive sequence current increase.

Apparatus for remotely protecting three phase electricity supply distribution transformers, comprising means for monitoring parameters of the supply in a distributor cable to the transformers;

• control means responsive to the monitored parameters to detect an increase in at least one selected function of said parameters which can be indicative of a fault current flowing in the distributor cable, to analyse any such increase to determine the likely existance and magnitude of any such fault current, and to generate a trip signal in accordance with said analysis;
• and circuit breaker means responsive to said trip signal to isolate the supply cable;
• wherein said control means is operative to detect an increase in the transient D.C. current flowing in any respective phase in addition to an increase in at least one other selected function which can be indicative of a fault current, and to analyse these increases by discounting any detected increase in said other function or functions occuring for as long as a detected increase in D.C. current in any phase remains.

Apparatus for remotely protecting three phase electricity supply distribution transformers, comprising means for monitoring parameters of the supply in a distributor cable to the transformers;

• control means responsive to the monitored parameters to detect an increase in at least one selected function of said parameters which can be indicative of a fault current flowing in the distributor cable, to analyse any such increase to determine the likely existance and magnitude of any such fault current, and to generate a trip signal in accordance with said analysis;
• and circuit breaker means responsive to said trip signal to isolate the supply cable;
• wherein said control means is operative to detect the two functions, negative sequence current and positive sequence current, and to analyse these by initiating generation of said trip signal in response to a detected increase in negative sequence current only if there is a simultaneous detected increase in positive sequence current in excess of a respective threshold increase.

Apparatus for remotely protecting three phase electricity supply distribution transformers, comprising means for monitoring parameters of the supply in a distributor cable to the transformers;

• control means responsive to the monitored parameters to detect an increase in at least one selected function of said parameters which can be indicative of a fault current flowing in the distributor cable, to analyse any such increase to determine the likely existance and magnitude of any such fault current, and to generate a trip signal in accordance with said analysis;
• and circuit breaker means responsive to said trip signal to isolate the supply cable;
• wherein said control means is operative to provide from the monitored parameters time related values for the positive sequence current, voltage and phase angle, to calculate therefrom time related values for the susceptance of the distributor cable and load connected thereto, to detect increases in the function, negative susceptance, and to analyse this increase by initiating generation of the trip signal if said detected increase exceeds a predetermined threshold.