- impedance on new base = old impedance x (new base / old base)
- impedance on 100 MVA = 0.16 x (100 / 0.8)
- = 0.16 x (125)
- = 20 per unit ( or 2000%) on 100 MVA.
What is Subtransient reactance of generator?
The subtransient reactance of a synchronous generator
How do you find the synchronous reactance of a generator?
- R
a
= Armature resistance. - X
s
= Synchronous reactance ( X
L
+ X
a
)
How do you calculate Subtransient reactance of a motor?
| Type of Motor Subtransient Reactance (per unit) Transient Reactance (per unit) | Induction ≤600 Volts 0.25 – | Induction >600 Volts 0.17 – |
|---|
What is the impedance of a generator?
The short-circuit impedance to be considered for this period is the transient reactance x’d expressed in % by the manufacturer. The typical value is
20 to 30%
.
How does a synchronous generator start?
In a synchronous generator,
a DC current is applied to the rotor winding producing a rotor magnetic field
. The rotor is then turned by external means producing a rotating magnetic field, which induces a 3-phase voltage within the stator winding. The rotor of a synchronous machine is a large electromagnet.
What is the formula for synchronous speed?
The synchronous speed of an AC motor is determined by the frequency of the source and the number of poles. The RPM is calculated by
multiplying the frequency times 60 and dividing by the number of pairs of poles
. This was explained in Chapter 6. Some motors are designed to operate at synchronous speed.
What is Subtransient?
What’s its origin? First, “subtransient” refers to
the fact that this quantity operates extremely fast
—faster than even “transient.” In technical terms, the subtransient time period lasts from about one to three cycles, which is from 16.7 milliseconds to 50 milliseconds (assuming a power frequency of 60 Hz).
What is a Subtransient fault?
The concept of Subtransient,
Transient and Steady State arises in case of fault in an Alternator
. … When the alternator is short-circuited, the currents in all the three-phases rise rapidly to a high value of about 10 to 18 times of full load current, during the first quarter cycle.
What is short circuit power factor?
Power factor (PF) is sometimes specified instead of X/R. This must be the short circuit power factor. Power factor is defined as the cosine of the angle between voltage and current. X/R is the tangent of this same angle. X/R can be found from power factor by taking the tangent of the inverse cosine of the power factor.
How do you calculate the fault current of a generator?
Fault current calculations are based on Ohm’s Law (V=I×R). To determine the maximum current available at any given point in a distribution system, the equation is rearranged to solve for current
(I=V÷R)
.
How do you calculate impedance of a generator?
impedance on new base
= old impedance x (new base / old base)
impedance on 100 MVA = 0.16 x (100 / 0.8) = 0.16 x (125) = 20 per unit ( or 2000%) on 100 MVA.
What percentage of buses in the power system are generator buses?
10 %
of buses in power system are generator buses.
What are the two types of synchronous generators?
Based on the armature winding and field winding arrangement, synchronous machines are classified into two types:
Rotating Armature type and Rotating Field
What is the principle of synchronous generator?
The principle of operation of synchronous generator is
electromagnetic induction
. If there exits a relative motion between the flux and conductors, then an emf is induced in the conductors.
What is difference between synchronous and asynchronous generator?
The difference between asynchronous and synchronous generator. A synchronous generator is
called “synchronous”
because the waveform of the generated voltage is synchronized with the rotation of the generator. … An asynchronous generator is essentially the same machine as an asynchronous or induction motor.
