Transformer redundant protection design
Transformer redundant protection design
(OP)
Hello,
The problem is following: we have 2 redundant numerical differential protection relays for a generator step up transformer.
Each numerical relay has it own separated 125 Vdc power supply and lockout relay.
There are 2 separate channels.
We receive only one dry contact (not 2) for each of the following protections:
- Pressure relief device
- Oil temperature trip
- frame temperature trip
- etc
How can we use these signals to trip both channel?
Can we send 50% of these signals on the Channel A and the other 50% on channel B?
In this case only one channel will trip each time.
The only solution i see is to duplicate the trip signals with auxiliary relays which must be supplied by a redundant power supply. To obtain redundant power supply, we will need a DC/DC converter (125Vdc/125Vdc) to provide galvanic isolation between the 2 independent 125VDc power supply.
I'am not sure introducing additional relays, DC/DC converter is the best solution.
What is the best practice?
Did you already meet this problem?
Thanks for your help.
The problem is following: we have 2 redundant numerical differential protection relays for a generator step up transformer.
Each numerical relay has it own separated 125 Vdc power supply and lockout relay.
There are 2 separate channels.
We receive only one dry contact (not 2) for each of the following protections:
- Pressure relief device
- Oil temperature trip
- frame temperature trip
- etc
How can we use these signals to trip both channel?
Can we send 50% of these signals on the Channel A and the other 50% on channel B?
In this case only one channel will trip each time.
The only solution i see is to duplicate the trip signals with auxiliary relays which must be supplied by a redundant power supply. To obtain redundant power supply, we will need a DC/DC converter (125Vdc/125Vdc) to provide galvanic isolation between the 2 independent 125VDc power supply.
I'am not sure introducing additional relays, DC/DC converter is the best solution.
What is the best practice?
Did you already meet this problem?
Thanks for your help.






RE: Transformer redundant protection design
Just an aside: you could diode auctioneer the two 125 V DC supplies. No need for a converter that I can see.
RE: Transformer redundant protection design
Specify why each of these would operate for a fault that the "Protective relays" would not, and you will see they will operate for either a non-fault, or they should be slower than the protective relays.
RE: Transformer redundant protection design
with your diode auctioneer you eliminate the security of 2 separate channels for protective relaying.
RE: Transformer redundant protection design
RE: Transformer redundant protection design
But try to distribute them wisely (e.g. Buchholz and PRD on different channels, oil and winding temps on different channels, Buchholz and RPRR on different etc.).
RE: Transformer redundant protection design
We will split the signals.
When paralleling two independent 125Vdc power supply diode, everything is ok until there is a ground fault.
Usually the voltage is -62.5 Vdc and +62.5 Vdc.
The two (-)of the power supply are connected together and the 2 (+) are paralleled with diodes.
If there is a ground fault on the (-) of one 125 Vdc circuit, the other one will also be affected.
Therefore we have considered a DC/DC converter with galvanic isolation.
I have an additional question.
If we need the generator breaker status for a redundant protection system with 2 separate channels and only one contact is available what is the solution if the customer can not supply a second contact?
Thanks for your help!
RE: Transformer redundant protection design
xnuke
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RE: Transformer redundant protection design
As you might guess, you need an auxiliary relay to multiply the GCB status, better have that a fast acting relay from a reliable manufacturer. You might consider connecting the GCB auxiliary contact directly to one protection channel (e.g. channel A) and the auxiliary contact in parallel. This way you don't get the time delay on the signal to channel A, only to channel B. But other design factors, i.e. regarding the possibility of a single failure bringing down both protection channels or both DC branches, might influence this. You might be facing the trade-off between time-delay on the GCB status signal and higher risk of double channel failure. Each additional component to your critical protection system adds complexity and failure probability. A second contact on the GCB is a far better solution IMO.
RE: Transformer redundant protection design
If so consider using a contact transfer module, like a SEL-2506. This is a very slick way of meeting 'galvonic seperation' requirements.
Mark
RE: Transformer redundant protection design
device.
Can the dual channel input device be configured for single channel input? I know on estop relays there was jumper settings to make it single channel input versus dual input channel.
If its customer driven to have 2 devices then you have to provide another seperate device to do the sensing since your device only has 1 contact output.
RE: Transformer redundant protection design
A second contact on the GCB is a far better solution IMO.
...to which I offer strong assent! The interposition of other devices where these can be avoided only increases the likelihood of a functional failure.
Also, dpc wrote:
Not sure of specific regulations for reliability, but I would probably just split them [gas trip, oil temp trip, frame temp trip, etc.] between the A and B side lockout relays.
Which leads me to respond:
I'm curious about "specific regulations for reliability" as well; in my utility, transformer protections are not typically dual-redundant, other than for some of the largest / highest-rated / mission-critical equipment. For most equipment therefore the various protective devices are grouped in such a way that one complete protection can be removed from service while the remaining scheme affords "adequate" interim equipment protection for the duration of the work. How the standard for "adequate" protection in these instances is derived is above my pay grade...
IEEE standards? Customer-driven? Local AHJ?
RE: Transformer redundant protection design
RE: Transformer redundant protection design