Transformer inrush current detector
First Claim
1. A power transformer protection system, comprising:
- a first Rogowski coil positioned to sense a primary current associated with a primary of the power transformer and to output a primary signal indicative of the primary current;
a second Rogowski coil positioned to sense a secondary current associated with a secondary of the power transformer and to output a signal indicative of the secondary current;
a protection relay configured to isolate the power transformer when the protection relay is activated; and
a controller operable to activate the protection relay,wherein the controller is further operable to compare the output of the first Rogowski coil and the output of the second Rogowski coil to obtain a differential first time derivative of current, to sample the differential first time derivative of current based on a sampling rate, to detect an inrush condition when a predetermined number of sequential samples of the differential first time derivative of current are within a predetermined range, and to prevent activation of the protection relay in response to detecting the inrush condition.
3 Assignments
0 Petitions
Accused Products
Abstract
A differential protection system for power transformers using Rogowski coils as current sensors can support an inrush current detection method based on sensing lows in the derivative of the sensed current. Effective detection of power transformer inrush conditions can enable blocking of a protection relay during inrush where the differential current may exceed a differential threshold value indicative of a fault without the presence of an actual fault. The outputs of the Rogowski coils, being proportional to the first time derivative of the sensed current, may be useful in the inrush detection method. Also, with reduced saturation concerns, the Rogowski coil protection system may employ a single slope response with increased sensitivity. A discrete time sampling technique for identifying low di/dt portions within the sensed current also may be useful in detecting power transformer inrush conditions.
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Citations
30 Claims
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1. A power transformer protection system, comprising:
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a first Rogowski coil positioned to sense a primary current associated with a primary of the power transformer and to output a primary signal indicative of the primary current; a second Rogowski coil positioned to sense a secondary current associated with a secondary of the power transformer and to output a signal indicative of the secondary current; a protection relay configured to isolate the power transformer when the protection relay is activated; and a controller operable to activate the protection relay, wherein the controller is further operable to compare the output of the first Rogowski coil and the output of the second Rogowski coil to obtain a differential first time derivative of current, to sample the differential first time derivative of current based on a sampling rate, to detect an inrush condition when a predetermined number of sequential samples of the differential first time derivative of current are within a predetermined range, and to prevent activation of the protection relay in response to detecting the inrush condition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for detecting inrush current of a power transformer, comprising the steps of:
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sensing a primary first time derivative of current using a first Rogowski coil; sensing a secondary first time derivative of current using a second Rogowski coil; comparing the primary first time derivative of current and the secondary first time derivative of current to determine a differential first time derivative of current; sampling the differential first time derivative of current; and determining the existence of an inrush condition in response to the sampled differential first time derivative of current. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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20. A method for differential protection of a power transformer, comprising the steps of:
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sensing a primary first time derivative of current using a first Rogowski coil; sensing a secondary first time derivative of current using a second Rogowski coil; sampling the primary first time derivative of current to obtain a first sample; sampling the secondary first time derivative of current to obtain a second sample; comparing the first sample and the second sample to determine a differential first time derivative of current; repeating the sensing, sampling, and comparing steps to obtain a plurality of differential first time derivatives of current; determining an existence of an inrush condition in response to a predetermined number of sequential differential first time derivatives of current being within a specified range; and blocking operation of a protection relay in response to a determination of the existence of an inrush condition. - View Dependent Claims (21, 22, 23, 24)
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25. A power transformer protection system, comprising:
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a first Rogowski coil positioned to sense a primary current associated with a primary of the power transformer and to output a primary signal indicative of the primary current; a second Rogowski coil positioned to sense a secondary current associated with a secondary of the power transformer and to output a signal indicative of the secondary current; a protection relay configured to isolate the power transformer when the protection relay is activated; and a controller operable to activate the protection relay, wherein the controller is further operable to compare the output of the first Rogowski coil and the output of the second Rogowski coil to obtain a differential first time derivative of current, to sample the differential first time derivative of current based on a sampling rate, to detect an inrush condition when a predetermined number of sequential samples of the differential first time derivative of current are in a substantially flat portion of a cycle, and to prevent activation of the protection relay in response to detecting the inrush condition. - View Dependent Claims (26, 27, 28, 29, 30)
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Specification