Distributed frequency relay

Details Distributed frequency relay Distributed frequency relay

1998-10-01

2001-11-06

Assouad, Patrick (Department: 2857)

Data processing: measuring, calibrating, or testing

Measurement system in a specific environment

Electrical signal parameter measurement system

C700S296000, C307S129000, C324S076390

Reexamination Certificate

active

06314378

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a method of increasing the electricity supply network stability without increasing its spinning reserve. This is achieved using one or more systems of distributed frequency relays.
BACKGROUND OF INVENTION
Traditionally electricity system stability has been provided by spinning reserve, which is spare generating capacity available to the system should unexpected loads, such as a large fault, threaten system stability. Spinning reserve is expensive as it does not produce any revenue for the generating company but it is required for system stability.
Attempts have been made to supplement the stabilizing effect of spinning reserve with fixed frequency relays fitted to major loads or sub-stations within a network. These relays disconnect their loads if the system frequency (nominally for example 50 hertz) drops too much indicating a system disturbance such as a major fault. The loads are then reconnected when the system has stabilised. The major disadvantage of this arrangement is its inflexibility. The dynamic nature of the loading on a network means that over time the network will require different stabilizing tactics which cannot be accommodated satisfactorily by the fixed parameters of these frequency relays.
SUMMARY OF THE INVENTION
An object of the present invention is the provision of an improved method of increasing an electricity supply network's stability, which minimises the above mentioned problems.
The present invention provides a method of increasing the system stability of an electricity supply network, said method including locating programmable frequency sensitive relays at load shedding points within said network, wherein each said relay controls one or more loads connected to said network and contains programmable disconnect and reconnect conditions such that one or more said loads are disconnected from said network upon said relay detecting said programmable disconnect conditions on said network, and such that one or more said loads are reconnected to said network upon said relay detecting said programmable reconnect conditions or said network.
Preferably said method includes providing a network stability manager with the ability to change or update said programmable disconnect and reconnect conditions by a communications link to said relays.
Preferably said load shedding points include any one of the following groups: sub-stations; factories; office buildings; households; plant; appliances; and a combination of these.
Preferably said programmable disconnect conditions include: low frequency disconnect levels; high frequency disconnect levels; rate of increase or decrease of frequency disconnect levels; a combination of these. Said relays can include a delay period or minimum duration of said condition prior to said disconnection.
Preferably said programmable reconnect conditions include: low frequency reconnect levels; high frequency reconnect levels; rate of increase or decrease of frequency reconnect levels; expiration of a disconnection period; a combination of these. Said relays can include a delay period or minimum duration of said condition prior to said reconnection.
The ability to reprogram the programmable conditions of each relay allows the stabilizing effect which they produce to be maximised despite changing conditions on the network. This capability is of considerable importance to the authority managing the network and a considerable advantage over the fixed frequency relays currently available. Another advantage of the present invention is that it is not reliant on a real time communication link; for example, to disconnect loads in the event of a system emergency. In this instance the distributed relays operate according to their most recent programmable conditions update. A further advantage of this present invention is that it is not restricted to monitoring frequency changes alone but can monitor, for example, rate of change of frequency and react accordingly. Parameters such as rate of change of frequency can sometimes be as important as the change in frequency itself.
The relays can be used to control all the load with which they are associated by, for example, disconnecting/reconnecting all sub-station circuits. Alternatively they may incorporate, be incorporated into, or be used in conjunction with a load shed management facility. For example in the case of households as load shedding points, the load shed manager could be the device for the operation of appliances, utilities and services within a building of New Zealand patent application no. 280179 (PCT/NZ96/00110).
When used with load shed management, the relay will control only a pre-programmed part of the available load in response to a network condition. The controlled load may be reprogrammed by the network stability manager for example. As a further enhancement, the load to be controlled by the relay (and load shed manager) may be dependent on the type of condition detected on the network. Further, the relay may control more than one load or group of loads according to different programmable conditions. For example, a minor fault may only require hot water cylinders (or an equivalent load) in a domestic premises to be disconnected, while a major fault may require all power to the premises to be disconnected.


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