1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1.TITLE OF THE INVENTION:
DIRECTIONAL OVERCURRENT PROTECTION METHOD OF CIRCUIT
BREAKER
2. APPLICANT:
Name: SHANGHAI LIANGXIN ELECTRICAL CO., LTD
Nationality: China
Address: No. 2000 South Shenjiang Road, Pudong New District, Shanghai 201315,
China.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in
which it is to be performed:
2
Technical Field
The present disclosure pertains to the technical field of circuit breakers, and
specifically relates to a directional overcurrent protection method of a circuit
breaker.
Background Art
In the prior art, universal circuit breakers all have three-stage protection. In a
power supply network with a single power source, a selective action can be
implemented depending on the cooperative relationship between a setting
value and time limit for the action when a fault occurs. In an actual power
network, power may be supplied by a plurality of power sources. Especially
power transmission networks and some power distribution networks mostly
supply power by double-ended power sources. In such a dual power network
for power supply, when a fault occurs, the setting value and the action delay
alone cannot meet the requirements of selective tripping and may tend to
cause protection misoperation.
Chinese Patent CN106849034 discloses an overcurrent protection method
based on a closed-loop operation mode of a power distribution network for
identifying and removing an overcurrent fault from an object to be protected in
the power distribution network operating in the closed-loop mode. Specifically,
two fault currents are measured at both ends of the object to be protected,
phases of the two fault currents are calculated, respectively, fault directions at
both ends of the object to be protected are determined based on the phases of
the two fault currents, a position of the overcurrent fault is identified by
comparing the fault directions at both ends of the object to be protected, and
then the overcurrent fault is removed. According to this technical solution, the
problem of misoperation or inaction in a power distribution network operating in
a closed-loop mode is solved based on the closed-loop operation mode of the
power distribution network, and the overcurrent protection can be performed
quickly and reliably, thereby reducing the power failure range caused by a fault
of the power distribution network and shortening the power failure time in the
practical application. However, this technical solution requires two current
measuring devices to be installed on the two sides of the object, which leads to
an increased cost and is not conductive to the miniaturization of the size of the
circuit breaker product.
Summary
In view of the technical problem of failure in correctly selective tripping
depending on the setting value and the action delay and occurrence of a
misoperation in the above-mentioned prior art power supply network with dual
3
power network, an objective of the present invention is to provide a directional
overcurrent protection method for a circuit breaker, in which an overcurrent
direction can be determined by acquiring voltage and current signals in one
direction, whereby a tripping action can be correctly selected.
Technical Solutions
In order to achieve the above technical objectives, the present disclosure
provides a directional overcurrent protection method for a circuit breaker,
characterized by comprising the following several steps:
(1) fault direction determination, wherein firstly overcurrent is determined by
acquiring a current at an output side of the circuit breaker, and then a phase
difference of the fault current is calculated by an algorithm based on a voltage
and current in the circuit, where the phase difference represents a logical
direction of the fault current;
(2) fault arbitration, wherein it is compared whether the logical direction of
the fault current in the step (1) is consistent with a logical direction initially set
for protection, and then it is determined, according to the comparison result,
whether the circuit breaker needs to perform a fault removal action;
(3) performing a tripping action, wherein a tripping action is not performed if
the comparison result in the step (2) indicates that the logical directions are
consistent, and a tripping and opening action is performed by a tripping unit if
the comparison result indicates that the logical directions are different.
Further, the calculation of the phase difference of the fault current by an
algorithm based on a voltage and current in the circuit in the step (1) is carried
out by a method of obtaining a difference between time points at which
zero-crossings of a current and voltage of the same phase are measured and
converting the difference into a phase difference Φ.
For a power network with a 50 Hz system, the phase difference is calculated
with 20 ms (=1000ms/50) corresponding to 360 degrees.
For a power network with a 60 Hz system, the phase difference is calculated
with 16.6 ms (=1000ms/60) corresponding to 360 degrees.
Further, when -90° < Φ < 90°, namely, when the current flows in a forward
direction, it is indicated that the fault has occurred in a forward direction of the
circuit breaker.
When 90° < Φ < 270°, namely, when the current flows in a reverse direction,
it is indicated that the fault has occurred in a reverse direction of the circuit
breaker.
Advantageous Effects
4
In a directional overcurrent protection method for a circuit breaker according
to the present disclosure, the directional overcurrent protection can be
achieved only by means of an algorithm on the basis of the acquisition of a
voltage and current on an output side of the circuit breaker. Firstly, the direction
(orientation) of the fault current is measured, and then a presence or absence
of a fault is determined. Moreover, hardware costs are not increased because
it is only necessary to acquire the voltage and current at the output side of the
circuit breaker.
Detailed Description of the Embodiments
The present disclosure will be further described below in connection with the
embodiments.
In an embodiment according to the present disclosure, a directional
overcurrent protection method for a circuit breaker includes the following
several steps.
In the first step, a direction of a fault current is determined. Specifically, firstly
overcurrent is determined by acquiring a current at an output side of the circuit
breaker, and then a phase of the fault current is calculated by an algorithm
based on voltage and current values in the circuit, where the phase represents
a logical direction of the fault current.
Here, the calculation of the phase of the fault current by an algorithm based
on voltage and current values in the circuit is carried out by a method of
obtaining a difference between time points at which zero-crossings of a current
and voltage of the same phase are measured and converting the difference
into a phase difference Φ.
For a power network with a 50 Hz system, the phase difference is calculated
with 20 ms (=1000ms/50) corresponding to 360 degrees.
For a power network with a 60 Hz system, the phase difference is calculated
with 16.6 ms (=1000ms/60) corresponding to 360 degrees.
Calculation results are described below.
When -90° < Φ < 90°, namely, when the current flows in a forward direction,
it is indicated that the fault has occurred in a forward direction of the circuit
breaker.
When 90° < Φ < 270°, namely, when the current flows in a reverse direction,
it is indicated that the fault has occurred in a reverse direction of the circuit
breaker.
In the second step, fault arbitration is carried out. Specifically, it is compared
whether the logical direction of the fault current in the first step is consistent
with a logical direction initially set by a control program, and then it is
5
determined, according to the comparison result, whether the circuit breaker
needs to perform a fault removal action.
In the third step, a tripping action is performed. Specifically, a tripping action
is not performed if the comparison result in the step (2) indicates that the
logical directions are consistent, and a tripping and opening action is
performed by a tripping unit if the comparison result indicates that the logical
directions are different.
The above embodiments can be changed or modified by those skilled in the
art to which this patent pertains based on the disclosure and teaching of the
above description. Therefore, the present disclosure is not limited to the above
specific embodiments. Any obvious improvements, alternatives, or variations
made by those skilled in the art based on the present disclosure would fall
within the scope of the present disclosure as claimed.
In addition, although some specific terms are used in this specification,
these terms are intended for convenience of description only and do not limit
this patent in any way.
6
We claim:
1. A directional overcurrent protection method for a circuit breaker,
characterized by comprising following steps:
(1) determining a fault direction, wherein firstly an overcurrent is
determined by acquiring a current at an output side of the circuit breaker,
and then a phase difference of the fault current is calculated by an
algorithm based on a voltage and a current in a circuit, wherein the phase
difference represents a logical direction of the fault current;
(2) performing a fault arbitration, wherein it is compared whether the
logical direction of the fault current in the step (1) is consistent with a
logical direction initially set for protection, and then it is determined,
according to a comparison result, whether the circuit breaker needs to
perform a fault removal action; and
(3) performing a tripping action, wherein the tripping action is not
performed if the comparison result in the step (2) indicates that logical
directions are consistent, and a tripping and opening action is performed
by a tripping unit if the comparison result indicates that the logical
directions are different.
2. The directional overcurrent protection method for a circuit breaker as
claimed in claim 1, wherein the phase difference of the fault current is
calculated, by the algorithm based on the voltage and the current in the
circuit in the step (1), by a method of obtaining a difference between time
points at which zero-crossings of a current and a voltage of the same
phase are measured and converting the difference into a phase difference
Φ, wherein
for a power network with a 50 Hz system, the phase difference is
calculated with 20 ms (=1000ms/50) corresponding to 360 degrees; and
for a power network with a 60 Hz system, the phase difference is
calculated with 16.6 ms (=1000ms/60) corresponding to 360 degrees.
3. The directional overcurrent protection method for a circuit breaker as
claimed in claim 2, wherein
when -90° < Φ < 90°, namely, when a current flows in a forward
direction, it is indicated that a fault has occurred in a forward direction of
the circuit breaker; and
when 90° < Φ < 270°, namely, when a current flows in a reverse
direction, it is indicated that a fault has occurred in a reverse direction of
the circuit breaker.
7
4. The directional overcurrent protection method for a circuit breaker as
claimed in claim 1, wherein an initial setting of the logical direction for
protection in the step (2) is implemented by a control program.