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PRD is to prevent tank rupture in case of internal fault. When the transformer is fused on primary side, the speed of fuse operation removes any possibility of tank rupture. So, there is no need to provide PRD. Internal fuses are better for quick isolation of faulty transformer and are thus...

It could be the potential difference between the meter earth and the earth point for MV earth cable. R Raghunath

Thanks 'Waross' for that correction. I agree, the power supply at input terminals needs to be monitored for under/no voltage. R Raghunath

ACB with UV release - I expect the release to drop the ACB on sensing low voltage / no voltage at the output terminals of the ACB, in other words, on loss of voltage to the motor downstream. If yes, it is incorrect to monitor UPS output using UV release of ACB, right! R Raghunath

The international standards do specify (Over) Voltage factor for PTs. If the impedance earthed system has ground fault protection system that isolates the faulty feeder automatically, 1.9pu for 1min is stipulated. In case there is no automatic trip available, it shall be 1.9pu for 8 hours. R...

In case of High Resistance Grounded (HRG) system, there is a possibility of primary side ground fault protection picking up for a VT secondary ground fault, in case the neutrals of both primary and secondary of the VT are grounded and in case the ground fault protection is set sensitive. This...

By 'Earthing transformer' you mean a Zigzag winding transformer, I suppose. Normally, zigzag winding transformer is used to provide earth reference for an unearthed systems such as Delta tertiary side in the subject three winding transformer. I have seen Resistor being connected to the neutral...

Star/Broken Delta connection of PTs is used for sensing Ground faults by measurement zero sequence voltage. In such case, a resistor is placed across broken delta secondary terminals of the PT. I haven't seen resistors across secondaries of individual phase PTs. R Raghunath

You do get the interlocked circuit breakers in the market readily, for the purpose. The mains breaker trips automatically on mains failure (No-volt release). The DG breaker closes after confirming there is voltage at its input terminals. Mechanical interlock between the two breakers prevents...

Compatibility involves dimensional compatibility, input/output compatibility, features compatibility etc. I would get hold of the literature of both the models and draw a comparison, feature by feature, to confirm the compatibility. The other approach is to approach Basler technical support for...

It depends on the type of principle used for REF protection. In case of High impedance type, Class-X (or Class-PX) is recommended. If it is low impedance type (also known as Bias type), Class-P type is acceptable. More details can be found in the Relay literature. R Raghunath

Generally speaking, multi core CTs are the norm as these reduce space requirement and cheaper too. How many cores in one CT and further details are subject to engineering consultant design for the requirements and the CT supplier for practicability of CT design. R Raghunath

Thanks Muthu Sir for correcting me. R Raghunath

Rated Voltage factor of 1.2 continuous and 1.9 for 30s is recommended by IEC 61869-3 for VTs meant to be used in non-effectively earthed systems that include automatic tripping in case of SLG fault. R Raghunath

There is no difference in construction of the motor itself. Of course the Class-F/B motor needs to have bigger coolers. It is the customer choice that he wants to buy a Class-F insulated motor but insists the temperature rise of the motor at full load should not exceed the limits set for...

A ground fault in L2 phase results in L1 & L3 phase-to-ground voltages to go up. This can go as high as 1.9 times the rated voltage depending on the type of power system earthing. Hissing noise from L2 bushing in the switchgear panel suggests that there is partial discharge due to excessive...

"standard 20125/35000 GRD Y single bushing PT's" - yes. The system is ineffectively grounded and the overvoltage on healthy phases during an SLG fault will be addressed by selecting the voltage factor to be 1.9. "nomenclature of 34500/34500 GRD Y" - the rating says that phase-to-ground...

"...trip when unbalance and 1-phase open circumstance" - it is a misunderstanding to think the ground fault protection can maloperate on unbalanced load or on 1-phase open condition. Neither of these can result in current flowing between neutral and earth. In case of 4-pole breakers, the...

Theoretically Ground fault current level can be as high as (or even higher if there is generation close by) the three phase fault current level. But, ground fault currents in the field are always quite low due to the ground loop impedance (that includes impedance at the point of fault). Even...

If the cables are fire retardant type or if the cable trench is buried type, no separate fire protection needs to be considered. In case of built-up trench (made of either concrete or brick), filling the trench with sand after the cable laying is completed, will take care of protection against...