CALCULATION OF SUB-TRANSIENT, TRANSIENT, STEADY STATE REACTANCE – PART – 01

SUB-TRANSIENT REACTANCE Xd’’

It is the ratio of induced e.m.f on no load and the sub-transient symmetrical current.

SUB-TRANSIENT CURRENT

I’’ = Eo / Xd’’

TRANSIENT REACTANCE Xd’

It is the ratio of induced e.m.f on no load to the transient symmetrical r.m.s current.

TRANSIENT CURRENT

I’ = Eo / Xd’

STEADY STATE REACTANCE Xd

It is the ratio of induced e.m.f to the steady state r.m.s current.

STEADY-STATE CURRENT

I = Eo / Xd

Eo – is the r.m.s value of open circuit phase voltage.

Xd’’< Xd’ < Xd

APPLICATION OF Xd’’ AND Xd’

SUB-TRANSIENT REACTANCE Xd’’

It is used for determining the interrupting capacity of the circuit breaker.

TRANSIENT REACTANCE Xd’

It is used for relay setting and coordination.

CALCULATIONS SHORT CIRCUIT CURRENT & KVA – PART – 01 – PERCENTAGE REACTANCE

PERCENTAGE REACTANCE

Percentage reactance is the load phase voltage dropped in the circuit when a full load current is flowing in the system.

Shor circuit current is obtained by multiplying the full load current by 100/%X.

Percentage reactance = [Base kVA / rated kVA] * %X

Where %X of reactance at rated kVA.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 02 – PROBLEM

Single line diagram of a power system is shown in the figure. If a three phase fault occurs at the HV side of the transformer determine the short circuit current.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 03 – PROBLEM

Single line diagram of a power system is shown in the figure. If a three phase fault occurs at the HV side of the transformer determine the short circuit current.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 04 – PROBLEM

Single line diagram of a power system is shown in the figure. If a three phase fault occurs at the LV and HV side of the transformer determine the fault MVA.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 05 – PROBLEM

Two generating stations having short-circuit capacities of 1000 MVA and 800 MVA respectively and operating at 11kV are linked by an interconnecting cable having the reactance of 0.75 ohms per phase. Determine the short-circuit capacity of each station.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 06 – PROBLEM

Single line diagram of a power system network is shown in the figure. If a three phase symmetrical fault occurs at the section B. Calculate the short circuit current and fault MVA.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 07 – PROBLEM

Single line diagram of a power system network is shown in the figure. The CBs have each a rupturing capacity of 750 MVA. Calculate the reactance of the reactor to prevent the breakers being overloaded of symmetrical short circuit occurs on an outgoing feeder connected to A.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 08 – PROBLEM

Single line diagram of a power system is shown in the figure. If three phase fault occurs on the section bar two, calculate the short circuit MVA.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 09 – PROBLEM

Single line diagram of a power system is shown in the figure. 

If three phase fault occurs on any feeder near transformer secondary find the short circuit MVA fed to the fault.

CALCULATIONS OF SHORT CIRCUIT CURRENT & kVA – PART – 10 – PROBLEM

A generating station having N sections bus-bars each rated at Q MVA with a% reactance is connected to the tie-bar system through busbar reactance of b%. Determine the short circuit kVA if a three phase fault occurs on one section and also calculate the short circuit kVA and also find when N is very large.

SYMMETRICAL FAULT CALCULATIONS – PART – 20 – CALCULATION OF POST FAULT CURRENTS AND VOLTAGES & ONE PROBLEM

PROBLEM

A radial power system network is shown in the figure. Calculate the fault current and also calculate the voltage at 11kV bus during the fault.

SYMMETRICAL FAULT CALCULATIONS – PART – 19 – CALCULATION OF POST FAULT CURRENTS AND VOLTAGES & ONE PROBLEM

PROBLEM

Reactance diagram of power system network is shown in the figure. If the fault occurs at bus four, calculate the fault current and also calculate the post fault voltage in each bus and line currents.

SYMMETRICAL FAULT CALCULATIONS – PART – 18 – CALCULATION OF POST FAULT CURRENTS AND VOLTAGES & ONE PROBLEM

PROBLEM

For the circuit shown in the figure. If fault occurs at bus two, calculate, the fault current and also calculate the post fault voltages and line currents.

SYMMETRICAL FAULT CALCULATIONS – PART – 17 – CALCULATION OF POST FAULT CURRENTS AND VOLTAGES & ONE PROBLEM

PROBLEM

For the circuit shown in the figure. If the fault occurs at the load terminals calculate, the transient fault current including the fault current and actual current.