GE DFF1000 Series, Инструкция по эксплуатации

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GEK – 106166B
5
1. 1. 1. 1. GENERAL DESCRIPTION AND GENERAL DESCRIPTION AND GENERAL DESCRIPTION AND GENERAL DESCRIPTION AND
APPLICATION
APPLICATION APPLICATION
APPLICATION
During the last years new technologies have allowed a significant advance in the concept of integration between
different components of the electrical system. The reasons for such integration are several:
-Reduce the investment in new equipment.
-Optimize the use of the existing installations.
-Improve the energy management system.
This integration of functions not only includes the switchgear protection and control devices, but also the
monitoring elements, the alarm signalling equipment (with its associated treatment) and finally the analysis off all
the available information (events, alarms, oscillography, load and demand profiles, etc.).
The DFF is a microprocessor based protection relay used for frequency supervision in an electrical system. It
allows to create a customer-defined load shedding scheme.
Frequency variations are originated by unbalance conditions between generation and load. The main reasons for
this condition are:
•
Inadequate load forecast or deficient generation capacity programming.
•
Busbars, generator group or interconnection feeders trip.
•
System split in different portions.
When the frequency variation is small, the unbalance condition will be corrected by the generator’s regulator. On
the contrary, in case of big frequency variations the regulator is not able to correct them itself, and the frequency
value will decrease with the danger of losing the generation capacity because of underfrequency tripping.
If this underfrequency condition is not corrected on time a general blackout may occur.
In case of shortage of generation capacity, the only possible way of recovering the stability of the system is
through a selective load shedding scheme. The load disconnection is done when the frequency goes down bellow
certain thresholds in order to provide reaction time to the generators, by means of the primary speed regulators.
It is important to point out that when the frequency decreases quickly the underfrequency condition is not enough
to recover stability. In this case the load shedding scheme must also take into account the frequency change rate.
This is done by calculating the frequency derivative over time. Loads are “shed” based not only on an absolute
(static) underfrequency threshold, but also on the dynamic frequency change rate.
The DFF is mainly used in medium voltage and distribution substations in order to implement a selective non-
critical load shedding scheme. By doing so, frequency recovers stability and we avoid potentially dangerous
situations that might affect generators or other parts of the electrical system.
The DFF available functions are:
a) Protection
•
Eight underfrequency units, programmable as absolute or change rate values.
•
Voltage unit to supervise frequency units.
•
Undervoltage unit (Note: All protection functions use phase B for calculation).
•
Overvoltage unit (Note: All protection functions use phase B for calculation).