Arcteq AQ-F210, Инструкция по эксплуатации

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Instruction manual –AQ F210 Feeder Protection IED 40 (292
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the current transformer rated primary and secondary currents. In case of motor or any
specific electrical apparatus protection the relay needs to be told also the motors nominal
current in order that the settings can be per unitized to apparatus nominal not to CT nominal
(This is not absolutely mandatory, in some relays it is still needed to calculate correct
settings manually. Setting the relay nominal current makes the motor protection a lot easier
and straight forward. In modern protection IED like AQ-2xx series devices this scaling
calculation is done internally after the current transformer primary, secondary and motor
nominal currents are given). Also in the AQ-2xx series feeder protection IEDs the scaling
can be set according to protected object nominal current.
Normally the primary current ratings for phase current transformers are 10A, 12.5A, 15A,
20A, 25A, 30A, 40A, 50A, 60A and 75A and their decimal multiples, while normal secondary
current ratings are 1 and 5A. For AQ-2xx series devices also other, non-standard ratings
can be directly connected since the scaling settings are flexible in large ranges. For ring
core current transformers the ratings may be different. Ring core current transformers are
commonly used for sensitive earth fault protection and their rated secondary may be as low
as 0.2 A in some cases.
In following chapter is given example for the scaling of the relay measurements to the
example current transformers and system load.
4.1.1.1 CT
SCALING EXAMPLE
The connection of CTs to the IED measurement inputs and the ratings of the current
transformers and load nominal current are as in following figure.
Figure 4.1.1.1-2 Example connection.