Hello,
While reviewing drawings from an (old) existing substation, I have come across a number of tripping circuits where auxiliary relays (normally GE HFA51A type) are used in an arrangement I cannot quite understand.
These auxiliary relays are used in Busbar Diff and CBF circuits, where...
I am having certain difficulty to understand how the delay Line of the TRV envelope curves specified in standards such as IEEE Std C37.04 is to be interpreted against a prospective TRV for a breaker in a substation.
In the standards ( for example IEEE C37.04) it is explained that this line...
Hello,
When several sets of current transformer are mounted on a bushing I have seen them marked as X, Y,(Z, W ...). However it is unclear to me what is what are the relative position of these marking within the bushing. That is: I have seen manufacturer drawings (for CBs with bushing CTs) where...
Hello,
I can see that the standard duty cycle for circuit breakers is well documented and can be found for example on the breaker nameplate. However this standard rating appears to cover two closing operations. What is unclear to me is what happens when we reach the last "open" of the sequence...
Hi,
I am trying to replace an old analog voltmeter installed in a synch panel. The reason for doing so is that the ratio of the VT connected to this device has changed. I would like to replace it by another one as similar as possible to the original.
Going through different catalogs of analog...
Hi,
I would appreciate it very much to know your opinions on the following subject:
We are modifying an existing electromechanical busbar tripping circuit, and we would like to segregate the new trip contacts by means of a blocking diode. The control voltage is 125Vdc.
The new tripping branch we...
Hi
I am trying to understand how to calculate the loadability of a distance scheme that uses a basic POTT (permissive overreach, looking into the forward direction with no modifications such as echo, weak infeed logic etc) scheme. I am focusing on a simple case of a two ended line with no taps...
Hi,
I would appreciate very much to have your opinion on the following:
I am trying to set a directional ground instantaneous element (34.5kV Line Prot. Application). The utility policy on this regard is that it should be set as "1.25 x 3Io for the maximum line end fault, with the remote end...
Hi!
I need to specify a current transformer that is to be connected to the neutral of an existing 34.5kV : 4.16kV (delta - wye) power transformer. The CT is intended for installation at the wye neutral connection (4.16kV side) which is directly connected to ground.
In principle I was thinking...
Hi,
I am trying to figure out when the use of 1A rated secondary CTs (rather than the more standard in the US 5A CT) could be benefitial in projects, when trying to avoid saturation in situations of high short circuit currents - systems with high X/R.
So far the impression that I got was that...
Hi,
I would appreciate it very much to have your view on the following: I am looking at the settings of a 51V-C (Voltage Controlled) element used for system backup protection in a Small Synchoronous Generator of a Hydro installation. Several sources I have been looking at (most importantly IEEE...
Hi,
I am trying to study the short circuit contribution of an Induction Generator. Even if the S.C. current will be sustained during a brief period of time, I would like to assess the amount of current it will be able to deliver.
I have the generator hort circuit reactance (Xd'') which I...
Hello,
Whilst going through the transformer standard requirements stated in IEEE C57.12.00 I have found the following statements related to their capability:
"Transformer shall be capable of [...] operating above rated volts or below frequency, at maximum rated kVA" when:
- The secondary voltage...
Hello,
I am trying to select a suitable S.A. for a 245kV substation. After going through ABB and Siemens papers on S.A. selection one of the main hilighted factors for the selection is the "lightning intensity" of the area. However I haven´t been able to find any reference defining what is...
Hello,
I am trying to prepare a VT specification and have come across what I believe is a pretty standard issue:
IEC 60044-2 sets the accuracy clases for burdens ranging from 25% to 100% of the VT rated burden. However the burden of new protection and metering devices that have to be connected...
