On high voltage circuit breaker schematics there are circuit breaker auxiliary switches S1, S2, S3, S4. All can be normally open, normally closed, late break, early make. But what is the difference between them? The only explanation that I have found anywhere states the following:
Auxiliary...
So, the main principles of interlocking are:
1. You can't operate disconnector unless associated circuit breaker is open;
2. You can't close earth switch unless associated disconnector is open;
3. You can't Close the disconnector while the associated earth switch is closed to earth;
This can...
Gas insulated equipment containing high pressure compartments, e.g. 145kV and 72.5kV gas insulated switchgear is normally provided with “plug in” cable connectors.
The normal operating practice is that no work should be carried out on gas insulated High Voltage systems on one side of a gas...
I understand what multiplexing is, i.e. transmitting several different signals via one channel. I just want some practical examples.
1. Assuming we have 96F fibre cable, which comprises 96 fibre strands. We can either connect 96 relays via this fibre cable directly. Or we can connect all of...
When doing protection grading studies for HV and EHV networks usual grading margins are 200-350ms depending on relay types (fast numerical vs slow electromechanical) and circuit breaker types (fast new vacuum vs slow old oil). When doing protection grading on LV networks I believe the rule of...
If pilot multicore cable is installed next to a power cable there will be induced voltage within the pilot cable. The magnitude of
50 Hz induced voltage depends on:
(a) the distance between the power cable, or line, and the auxiliary cable;
(b) the magnitude of the current in the power circuit...
I understand that you need them to isolate tripping functions, but what would be the reason why you would want to isolate certain trip functions? Looking at attached circuit breaker DC schematic example:
LK10 (light blue) BUS ZONE TRIP ISOLATION - I assume you need to remove this link if you...
If you order high voltage SF6 indoor metalclad switchboard comprising several panels does it arrive on site from the manufacturer as a whole switchboard unit or as separate panels?
I understand transformer vector groups, however I get confused when it comes to changing phase order outside the transformer to change it's vector group. For example the following statement:
"For this connection the outer HV phase conductors are effectively swapped, with phase Red connected to...
When you have a dual ratio CT, say 1000/500/1, and the thermal rating of CT is 100%. Does this mean that on the 1000/1 ratio you will 1000 A thermal rating and on the 500/1 ratio you will have 500 A thermal rating. Or is thermal rating independent of the ratio you choose and it will be 1000 A in...
As per IEEE Std C57.32 section 6.4.2 extract below Earthing Transformer continuous rating must be 3% of 10s thermal rated current.
We will be installing ZNyn11 Auxiliary Earthing transformer for the purposes of limiting 132/33 kV YNd11 power transformer 33 kV side earth fault current to 1000...
So in order to provide start point reference on a delta winding of a power transformer and limit earth fault current to a certain level you can either use High Impedance Earthing Zigzag Transformer or Earthing Zigzag Transformer + Neutral Earthing Resistor. Does it matter which option you...
I often specify dual ratio CTs based on standards, however when producing multicore wiring diagrams I always choose the ratio which is closest to required load. I never really thought about it, but why do you actually need dual ratio CTs? Even if you have ONAN/ONAF/OFAF transformer where OFAF...
Can someone please explain when do you need current transformer in/out switch the one shown on the image below.
I have seen these on 132 kV high impedance differential protection schemes and 33 kV busbar protection schemes. I have also seen them on 132 kV transformer backup protection scheme...
Is there a source of information that outlines typical transformer X/R ratios depending on MVA and voltage rating?
Also would be helpful to have the same information for underground cables.
I mostly see dual ratio CT specs where only one set of parameters is shown. And I was always wondering if you can make out parameters for the lower ratio with given information or not. i.e.:
1. Knee point voltage. Based on the following formula Vkp = K * I(fault)/CTratio * (RCT + RL + RR) lower...
Just want to make sure that I am looking at the right thing. Protection relay output contact spec says the following:
Make & Break Capacity:
DC: 50 W resistive
DC: 62.5 W inductive (L/R = 50 ms)
AC: 2500 VA resistive (cos φ = unity)
AC: 2500 VA inductive (cos φ = 0.7)
I assume that if circuit...
