automatic load dropping (ALD) scheme

[dfopiso]

hello! the recently promulgated Grid Code in my country requires us to implement an ALD scheme in our system. we are currently implementing a substation automation project and we thought of integrating the ALD scheme via the frequency relay. is this possible? any suggestion, comment or website that can be referred will be highly appreciated. thanks in advance for your responses.

 

[SidiropoulosM]

Here in the USA we use two types of load shedding:
(1) underfrequency load shedding and (2) undervoltage load shedding. The first is used in almost every system. The second is used in load areas that are vulnerable to voltage collapse. The relays must have a time delay, usually 2 seconds, to avoid tripping for transient system swings. You can find extensive literature by doing a google search on the above topics (1) and (2). Michael Sidiropoulos

 

[nraju]

Suggestion:

Rather than an underfrequency relay, try using df/dt relay (rate of change of frequency) if possible.

 

[AAK]

Dafo74,
I worked in a power station where multi-step frequency relays were used for load shedding. Upon starting a new automation project (Network Control System) by Siemens, the alarms of these frequency relays were integrated with the system for information purpose. In addition to that a new load shedding system (software interfaced) was introduced utilizing Siemens SIMATIC S5 PLC where the options of manual or automatic load shedding was made available. The non critical loads could be put in any order (priority) in case of a generator loss or any unblance between the generation and load demand. The output would go to the relevant circuit breakers to trip after considering the amount of lost source and the available spinning reserve from the other sources.

I think for automation in general, try to identify any procedure/information being collected manually and consider them for the new system. Good luck. Best regards,
AAK

 

[jbartos]

Suggestion to nraju (Electrical) Feb 22, 2003 marked ///\\Rather than an underfrequency relay, try using df/dt relay (rate of change of frequency) if possible.
///The frequency slew rate is better to be added to the normal underfrequency load shedding since df/dt may be very, i.e. acceptable, however, the underfrequecy may be not tolerable, i.e. the load shed is necessary.\\

 

[dfopiso]

thanks for your replies! on the df/dt relay, is this function built-in if the frequency relay is microprocessor-based? if not, what brands do you recommend for the df/dt relay.

 

[dfopiso]

hello!
its been awhile but i still want to know if the df/dt is built-in function in microprocessor-based frequency relays.

 

[freelancer]

dafo74,

I have worked with ABB's RXFK 2H relay (which is a static microprocessor based frequency relay) in which underfrequency and df/dt are combined in one module.

 

[sanvapat]

dafo74,

one we are using for under frequency load shedding is ABB's SPAF relay. It is having flexibility of combining freq and df/dt in around 3 stages. i.e u can have 3 stages for, say alarm at 49 Hz+ 0.2 Hz df/dt...and so on for other stages.

 

[jbartos]

Suggestion: Visit

http://www.liebert.com/support/whitepapers/documents/bsc_ups.asp

http://www.liebert.com/support/whitepapers/documents/Part1Topology.pdf

http://home.att.net/~herb.alvarez/highnine.htm

for: slew rate justification

 

[jbartos]

Suggestion: Visit

http://business.vsnl.com/under_frequency_relay/

http://www.computecsrl.com.ar/cptraf_english/cptraf_description.htm

http://www.lntebg.com/mps/grid.html

etc. for more info
The numerical relays tend to have df/dt incorporated