Reverse Power Protection

You must determine if in any situation that the current can reverse flow and overload a circuit...

..."In simplified terms a relay that operates with current flowing only in one direction and not the other. Ie, current flowing forward above the trip threshold will cause a trip, current flowing in the reverse direction above the tripping threshold will do nothing."..

Yeah, but I cringe when the video guy talks about current flowing the wrong direction instead of power.

I know this falls short and is perhaps confusing as well, but it's the best one I came across...If you see something better feel free to post, or if you get particularly motivated you could make an informative video on this and/or related subjects...?...but no pressure...haha, I know you're so busy...like me....

Hey, except for the Current/Power "nit", I thought it was very well explained, better than I could have done.

I especially liked the description of the workings of the Reverse Power relay, basically, a multiphase AC motor that turns backward and closes contacts if the current/voltage phase relationship indicates reverse power.

I'm going to show my ignorance here, but can you expand on that Rixter?

AC ... Alternating Current.

In AC systems, current flows back and forth and voltage swings positive and negative. Power equals voltage times current. So power flows in the same direction that the current is flowing when the voltage is positive and opposite the current direction when the voltage is negative.

You expect us to guess a lot.....

Transformer rating ??

Generation :- 320KVA Diesel Generator (DG) + 20 kW solar = 340 kVA

Loads : 7 kW lighting + 80 kW [vrv ac system ??]

Reverse Power Relay: switches or trips what?? or is it for DG?

Must suppose transfo is > 340 kVA rating exporting all generation.

Grid Operators usually have detailed requirements about protection to be met before generation connection is permitted.

Reverse power [Grid to DG direction] with DG shutdown & disconnect time delay of seconds would be usual, also disconnect & shutdown at loss of synchronism/Grid. Motoring a diesel engine is not a good idea - mechanically it will not do it harm short term but what if there is no power because all the fuel is pouring onto the floor?

Particularly, they do not want your gen keeping their line live if it disconnects at their end - it makes trouble for them to reconnect and danger for their workers and public e.g. line wire on ground.

According to usual standards, 20 kW Solar PV controllers must have auto shutdown if Grid is lost.

To the Grid, your 87 kW load looks like "reverse" power - if generation [export] is normal.

DG may only take 40 kW when "motoring" [reverse power], so whole 415V monitoring cannot tell if DG is motoring or it is just normal loads.

I think the reverse power relay must trip off 415V breaker connecting DG to distribution board or transfo. Obviously, you want your load to be fed when DG is being maintained.

This is local code ENA_EREC_G99 for connecting generators of <1 MW to mains (DNO = Distribution Network Operator). It is >300 pages, not all applies to particular type/size generator..

http://www.dcode.org.uk/assets/files/Qualifying%20Standards/ENA_EREC_G99_Issue%201_Amendment_4_(2019).pdf

Section 10 is protection, particularly.....

<<10.3.1 Suitable protection arrangements and settings will depend upon the particular Generator installation and the requirements of the DNO’s Distribution Network. These individual requirements shall be ascertained in discussions with the DNO. To achieve the objectives above, the protection shall include the detection of:  UnderVoltage (1 stage);  OverVoltage (2 stage);  UnderFrequency (2 stage);  OverFrequency (1 stage);  Loss of Mains (LoM).>>

Considering your circumstances, I do not think power direction relay is reliable way of detecting loss of mains LoM, but is advisable [monitoring generator current & voltage for power flow] to protect genset.