When running power source fails, standby source supplies power to connected auxiliaries. The system, which transfers bus from running source to standby source and vice versa is called Bus Transfer System (BTS). Control and Solution can provide complete solution in this area.
An Automatic Bus Transfer System (ABTS) is ideal to meet the requirement of uninterrupted power supply for industrial and commercial facilities with critical processes (mentioned above).
It is a standard requirement of every industry to have one stand by power supply unit like, DG set, in case of the failure of the existing supply. If the existing power supply is tripped, one has to change over to another stand by unit by changing the grid. It is very much essential to transfer the grid safely and without any power interruption. The standards for the safe transfer of the grid supply are laid down in ANSI standard CS 0.41-77 (specifically covers the poly-phase induction motor). As per the standard, resultant of the present and new power shall not exceed 1.33 Volt/ Hz for 60 Hz source. As we work with 50Hz supply, to achieve uninterrupted power supply, the grid changeover is required to be done within 20 mili second (period of one cycle). Therefore, it is required to measure and compare phase angles of both the supplies at very high speed. The ANSI standards suggest that phase angle difference must be within 20 degrees for power grid change over for safe transfer.
The existing method uses the conventional relay-based system, wherein the international standards (mentioned above) are not followed. Due to lack of facility to compare the phase angle of two sources (required to have uninterrupted grid changeover), we cannot achieve the uninterrupted Bus Transfer with this method. Hence, is not recommended for the industry having critical processes. Another disadvantage of relay based system is we cannot have better operator interface like Man Machine Interface (MMI) at remote places, which is today’s requirement. Cierto Control And Solutions (I) LLP (CSIL) has developed a system to transfer the bus as per ANSI standard. The developed bus transfer system transfers bus within 50 to 60 ms (this time depend on on/off timing of circuit breaker and may be reduced, if breaker on/ off time is less). But this transfer is the safest transfer and will not cause any damage of connected auxiliaries due to phase difference in the existing and stand by power supplies. If we have circuit breaker, which have on/off time less than 20 ms, we can achieve bus transfer without any interruption in power supply. Hence, continuity of power is remains with safe and reliable transfer.