Hello all
I am modelling a VCB for transient studies and am a little confused. IEC62271 prescribes TRV tests on a 36kV breaker at a TRV rate of rise of 0,57kV/us, however the literature suggests that when modelling the VCB withstand a value of between 20-30V/us should be used. This is very...
Please can you help me understand something.
In the 4x4 world we often install a second battery in a vehicle to power fridges etc. This is normally connected to the charging circuit via an solenoid when the engine runs. If the second battery is very flat a very high charging current could flow...
Haven't been on the forum for a long time. Hoping I can get some advice.
A client is designing a network for a mine. The supply transformers are 2 x 80MVA 132/33kV Yd earthed via a NECR.
The 33kV is required due to the heavy load and can be considered as an intermediate voltage.
The mine and...
I am trying to find 'typical' undervoltage settings for a SCIM. I have very few details on the machines (they are pretty old) apart from 4MW, 6,6kV and application ward leonard mine winder.
I don't want to pre-empt but would imagine an UV level of 80%Un would be acceptable (yes/no? lower?) but...
Here’s the problem :
Network :
- 132/6,6kV 20MVA 10% Yd (earthed via NECR) supply transformer, giving LV fault level of 192MVA.
- 6x6,6kV 150mm^2 400m PILC feeders to Mill Substation. Mill SS feeds 2 x 5,5MW mills.
- Speed control is achieved by slip recovery via Alstom PWM drive in rotor...
Client has been having irregular 11kV VT failures on an submerged arc furnace installation. System details as follows:
- 2 x VTs per furnace 11/28/75kV connected phase to phase upstream of the furnace breaker.
- Supply transformer 88/11kV 75MVA.
- 4,8 MVAr plain capacitor bank switched with the...
Is it possible for ferroresonance to occur in the following scenario :
22/11kV 2MVA Dyn transformer, resistance earthed, no load on transformer. 1,1 MVAr plain capacitor bank connected at 11kV.
My understanding is that for ferrorresonance to occur there must be either an unearthed system or...
Some comments from those of you with experience on gensets would be appreciated.
Client has bought an AVK diesel generator with the following ratings:
6,6kV
5300kVA @ pf 0,83
1500rpm
Unfortunately I do not have any further detail at this stage as the whereabouts of the manuals are a mystery...
Our client has a 1650kW 6,6kV synchronous motor (on a minewinder ward leonard system). There are what appear to be discharge resistors mounted on top of the control panels (air cooled, wire wound, housing is approx. 1m3). Are these resistors definitely discharge resistors and will they make much...
Your opinions would be appreciated.
We have a client who is experiencing VT failures. The circuit is as follows :
- 88/11kV 75 MVA star/star supply transformer; HV & LV earthed via NER.
- Approx. 80m cable to sub. Furnace breaker (furnace fed via 3 x 1 phase trfrs).
- Surge arrestors are...
When referring to the NEMA curves regarding derating of machines due to negative phase sequence, what formula is used to determine the voltage unbalance ?
Vub = (Max - Ave)/Ave x 100
or
Vub = V2/V1 x 100 (neg seq/pos seq)
Both would give different answers the way I see it. Seems to me...
A client of ours has had multiple LV (525V) motor failures since the plant was commissioned (a large smelter).
Our system measurements (over a two week period) show no abnormalities on the system.
Examination of 5 failed motors shows various symptoms (2 rust, 1 interturn, 2 insulation).
Does...
We have a 6,6kV 6MW 6/12 pulse thyristor Mine Winder with a 3,1 MVAr 3rd order damped filter (Resistor and decoupling capacitor across the reactor) tuned at 4,8p.u. connected to the same busbar (no other loads). Acceleration of the winder peaks the load at about 15MVA.
Measurement at approx...
Which fault current is to be used for coordination of IDMT overcurrent relays - 1/2 cycle symmetrical or interrupting current (4-5 cycles, 50Hz). I am using the IEC 60909 method of determining scct currents (EDSA software).
I have been through many standards (IEEE color books) and cannot find a...
As I understand it the breaking capacity of an IEC breaker is given by the "rated short circuit breaking" current in kVrms. My queries :
- Must the DC component be considered when determining whether an installed breaker rating is being exceeded, or is the rating a symmetrical rating...
I am trying to find out what manufacturer/type of fuses were used in the Tiger ring main units (11kV). I am doing a protection coordination where I have come across one (90A).
Thanks
Searching for opinions with this one.
We are doing a study on an existing plant and have found the symmetrical breaking capacities of some indoor metalclad Hawker Siddeley 11kV OCBs to be marginal (18,4kA). The prospective breaking fault current has been considered at 5 and 10 cycles (50Hz)...
Can anyone help me with a copy of obsolete CT standard BS3938-1965 or if this is not possible, more specifically the following :
- What is the primary continuous current rating as specified by the standard. Is it simply the primary rated ratio current or is there an overcurrent factor ?
- I need...
