Ice NP900 Series, Инструкция по применению

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Application Guide - NP900 Series 21 (504
)
For the measurements to be correct there is need to make sure that the measurement
signals are connected to correct inputs and direction of voltages is connected correctly
and the scaling is set correctly.
For the scaling the relay calculates scaling factors based into the set VT primary and
secondary voltage values. Relay measures secondary voltages which in this case mean
the voltage outputs from the voltage transformer that is installed into the primary circuit of
the application. Voltage can be measured up to 400V system directly as well. In order the
relay to “know” primary and per unit values it needs to be set the voltage transformer rated
primary and secondary voltages. In modern IEDs like NP900 series devices the scaling
calculation is done internally after the voltage transformer primary and secondary voltages
are given.
Normally the primary line to line voltage rating for voltage transformers between 400V and
600kV while normally secondary voltage ratings are 100-120V. For NP900 series devices
also other, non-standard ratings can be directly connected since the scaling settings are
flexible in large ranges.
In following chapter is given example for the scaling of the relay measurements to the
example voltage transformers.
3.1.2.1 VT
SCALING EXAMPLE
The connection of VTs to the IED measurement inputs and the ratings of the voltage
transformers are as in following figure. In figure below line to neutral voltages are
connected among with zero sequence voltage. Other connection possibilities are
presented in this chapter.