* (Number of SCRs in string)
When η = 1 each SCR in string has 100% identical characteristic or utilization of thyristor will be maximum. But it is not possible practically.
|
Voltage across each of remaining (n – 1) SCRs = (n – 1) I2R
For a string voltage Vs, the voltage equation for the series circuit will be
Vs = I1 R + (n –1)I2 R
= Vbm + (n – 1) R [I1 – (Ibmx – Ibmn)]
let (Ibmx – Ibmn) = ΔIb
RI1 = Vbm
When current required by the load is more than the rated current of a single thyristor, SCRs are connected in parallel in string. For equal sharing of currents V-I characteristics of each SCRs during forward conduction must be identical as far as possible.
For parallel-connected SCRs, voltage VT across them must be equal. Figure (b) show that for a same voltage drop VT, SCR1 shares a rated current I1 whereas SCR2 carries current I2 much less than rated current I1. The total current carried by the unit is I1 + I2 and not the rated current 2I1 as required. Therefore string efficiency is given by:
Protection of a device is an important aspect for its reliable and efficient operation. Silicon Controlled Rectifier (SCR) are a very delicate semiconductor device. SCR may face different types of threats during its operation due to over voltages, over currents etc. There are different types of thyristor protection schemes available for satisfactory operation of the device like:
5 videos|50 docs|46 tests
|
1. What is series operation of SCR? |
2. What is parallel operation of SCR? |
3. What are the advantages of series operation of SCR? |
4. What are the advantages of parallel operation of SCR? |
5. Can SCRs be operated in both series and parallel configurations simultaneously? |
|
Explore Courses for Electrical Engineering (EE) exam
|