Electricity: electrical systems and devices – Safety and protection of systems and devices – Feeder protection in distribution networks
Reexamination Certificate
1999-12-29
2002-04-09
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Feeder protection in distribution networks
C361S064000, C361S066000
Reexamination Certificate
active
06369995
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a protection relay device for the distribution equipment of a distribution system having a hierarchy of branches.
FIG. 5
is a diagram showing the system structure of the conventional distribution system described in the Institute of Electric Engineers of Japan, Technical Study Report, No. 469, p 28, which uses a timing different protection relay device and has a hierarchy of branches coupled to a power source. This distribution system includes branches
8
to
10
of the hierarchy structure coupled to a power source
1
, a current transformer
4
A for detecting total current flowing through the higher-rank branch
8
, and a relay
3
A which determines whether or not a short-circuit failure has occurred in a path from the higher-rank branch
8
to the downstream thereof on the basis or current value detected by the current transformer
4
A and operates a breaker
2
A for cutting off the current flowing through the higher-rank branch
8
at the time where it is determined that the short-circuit failure has occurred in the path.
This distribution system further includes a current transformer
4
B for detecting total current flowing through the middle-rank branch
9
, and a relay
3
B which determines whether or not a short-circuit failure has occurred in a path from the middle-rank branch
9
downstream thereof on the basis of the current value detected by the current transformer
4
B and operates a breaker
2
B for cutting off the current flowing through the middle-rank branch
9
at the time where it is determined that the short-circuit failure has occurred in the path. Further, this distribution system includes a current transformer
4
D for detecting total current flowing through the lower-rank branch
10
, and a relay
3
D which determines whether or not a short-circuit failure has occurred in a path from the lower-rank branch
10
or downstream-thereof on the basis of the current value detected by the current transformer
4
D and operates a breaker
2
D for cutting off the current flowing through the lower-rank branch
10
at the time where it is determined that the short-circuit failure has occurred in the path.
This distribution system further includes a current transformer
4
E for detecting total current flowing through a lower-rank branch end
11
, and a relay
3
E which determines whether or not a short-circuit failure has occurred at the lower-rank branch end
11
on the basis of the current value detected by the current transformer
4
E and operates a breaker
2
E for cutting off the current flowing through the lower-rank branch end
11
at the time where it is determined that the short-circuit failure has occurred in the lower-rank branch end.
This distribution system further includes a current transformer
4
C for detecting current flowing through the predetermined position of a system branched from the higher-rank branch
8
, and a relay
3
C which determines whether or not a short-circuit failure has occurred in a path from the predetermined position or downstream thereof on the basis of the current value detected by the current transformer
4
C and operates a breaker
2
C for cutting off the current flowing through the predetermined position at the time where it is determined that the short-circuit failure has occurred in the path. Further, this distribution system includes a current transformer
4
F for detecting current flowing through another predetermined position downstream of the predetermined position, and a relay
3
F which determines whether or not a short-circuit failure has occurred in a path from the another predetermined position or downstream thereof on the basis of the current value detected by the current transformer
4
F and operates a breaker
2
F for cutting off the current flowing through the another predetermined position at the time where it is determined that the short-circuit failure has occurred in the path.
According to the distribution system thus arranged, the relays
3
A to
3
F are arranged to have different time periods for starting the operations after the occurrence of the short-circuit failure in accordance with the corresponding ranks of the system branches
8
to
10
thereby to discriminate the section where the short-circuit failure occurred, respectively.
For example, the operation time period required for operating (current cut-off operating) the corresponding one of the breakers
2
A to
2
F after the detection of the same current is set to be longest in the relay
3
A which is closest to the power source
1
and shortest in the relays
3
D,
3
E and
3
F which are disposed at the lower-rank end.
Thus, when the short-circuit failure occurs, the breaker at the higher-rank side among the breakers closest to the section where the short-circuit failure has occurred operates at first thereby to cut off the current supplied from the power source
1
. For example, when the short-circuit failure occurs at the lower-rank branch
10
of the relay
3
D, although each of the relays
3
A,
3
B and
3
D detects the excessive current, the relay
3
D having the shortest operation time operates the breaker
2
D to cut off the current at the earliest time point as compared with other relays.
Further, when the short-circuit failure occurs at the higher-rank branch
8
between the relay
3
A and the relay
3
B, the relay
3
A detects the excessive current and operates the breaker
2
A to cut off the current upon the lapse of the set operation time period.
In the aforesaid conventional protection relay device for distribution equipment, when a short-circuit failure occurs at the higher-rank branch
8
nearest to the power source
1
, a large excessive current is generated and such phenomena as a voltage drop, an instantaneous power failure or the like influences a wide area of the lower-rank system. However, since the operation time period of the relay
3
A is set to be longest, the time period required for the breaker
2
A to operate after the occurrence of the short-circuit failure is long.
As a consequence, there arises a problem that the short-circuit failure continues for a long time and so the distribution equipment may be broken and the operation of the devices connected to the distribution equipment may be stopped.
Further, in the case where the number of the branches of the system increases, there arises a problem that, since the operation of the breakers of the higher-rank is further delayed, it is required to adjust the operation time periods of all the relays again.
As a technique relating to the aforesaid protection relay device for a distribution equipment, the Unexamined Japanese Patent Application Publication No. Hei. 7-322470 discloses “Protection Relay Central Management Device” wherein a central control device is coupled to a plurality of protection relays through a transmission path and the central control device collectively manages the operation states of the plurality of the protection relays. Further, as another technique relating to the aforesaid protection relay device for a distribution equipment, the Unexamined Japanese Patent Application Publication No. Sho. 58-119725 discloses “Protection Relay System for Non-Utility Transformation Equipment” wherein a protection relay is disposed at a portion within premises, terminal devices are provided at various portions of the premises, the terminal devices send current and voltage information and breaker information to the protection relay, and the protection relay collectively performs the calculation for protecting the respective equipment within the premises to determine the breaker associated with the failure and to trip the breaker directly or through the terminal device.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforesaid conventional circumstances and an object of the invention is to provide a protection relay device for the distribution equipment which can determine a short-circuit failure section without differentiating the operation time periods among relays and remo
Kagawa Kazuhiko
Moritoh Eiji
Jackson Stephen W.
Leydig , Voit & Mayer, Ltd.
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