Earth Reactor Calculation 1

[PowerV]

How can calculate the size of the neutral earth reactor required if I have a 65MW Power Transformer Star-Delta 110/20kV. 50Hz. Is 500A 30s correct? with 300A CT´s. Thanks

 

[SMB1]

In order to specify the rating of a neutral grounding reactor, the value of its reactance (Xn),
the system frequency (f), the system line-to-line rms voltage (E), and the sequence impedances
to a ground fault at the reactor location (Z1, Z2, Z0) have to be known if the fault current
is to be calculated. The rating of the reactor shall include the following:
(1) Rated Current (It). This is the current through the reactor during a ground fault at the
reactor location.

It=root 3 * E/(2Z1+j(X0+3Xn))

(2) Rated Voltage (V). This is the product of the reactor current and reactance Xn of the
reactor at system frequency. This voltage shall be as specified in Table 4 of IEEE Std
32-1972 [4].
(Eq A10)
(3) Frequency (f). This is the system frequency.
(4) Basic Impulse Insulation Level (BIL). The BIL of the neutral reactor is as specified in
Table 4 of IEEE Std 32-1972 [4]. See also Section 3.8.3 of IEEE Std C62.2-1987 [6], or
IEEE Std C62.11-1987 [7].
(5) Circuit Voltage of the System (E). This is the system line-to-line rms voltage.
(6) Insulation. Insulation is oil, dry, or gas insulated.
(7) Service. Service is either indoor or outdoor.
(8) Rated Time. Rated time is the time during which the reactor will carry its rated thermal
current (It), and it shall be either 10 s, 1 min, 10 min, or extended time.