For series connected SCRs, static equalization is obtained with the help of

Static equalization circuit:

• When two SCR have connected in series in forwarding blocking mode, then voltage distribution across each SCR is unequal.
• In order to make voltage distribution uniform, the static equalizing circuit is used in which a resistance is connected in parallel with each SCR.

​The value of resistance 'R' is given by:

\(R = {nV_{bm}-V_s \over (n-1)Δ I_b}\)

where, n = No. of SCR connected in series

V_bm = Maximum blocking voltage

ΔI_b = Blocking state current

Dynamic equalization circuit:

• The factor which is responsible for unequal distribution of voltage in the reverse biased condition is the junction capacitance of the SCR. This junction capacitance is also known as the self-capacitance of the SCR.
• Since the capacitance is different for different SCR, so the voltage across each SCR also differs.
• Therefore, the value of the discharging current may be very high. Therefore, to limit the discharge current, a limiting resistance R_C is connected in series with the shunt capacitor.
• A combination of R_C and capacitor (C) is called a dynamic equalizing circuit.