FAQs
You will find answers to the most frequently asked questions below.
Does NTC have office in Tehran? If yes, where is it?
Answer: Yes.
P.O.Box. 14335-899
No. 1206- Sarve Saii building- Valie-asr street
Tehran- Iran
Tel. : +98-021-88701414
Fax. : +98-021-88701415
P.O.Box. 14335-899
No. 1206- Sarve Saii building- Valie-asr street
Tehran- Iran
Tel. : +98-021-88701414
Fax. : +98-021-88701415
How can I contact relevant persons in NTC?
Answer: Please click here
How can I determine my requirement regarding the rated current of CT?
Answer: Rated current of CT is equal to the rated current of the network in which the CT is to be installed considering future developments.
How can I determine the rated burden of each secondary?
Answer: The rated burden of CT/PT is determined equal to the sum of actual burdens connected to it + 50% extra burden. If more than the a.m. value is ordered, the accuracy may be deteriorated in addition to the expenses of the overdesign.
How can I order for NTC products?
Answer: Please click here
How the cables to be connected to the secondary terminals are brought in the terminal box?
Answer: In medium voltage, there are cable glands on the terminal box through which the cuotomer’s cables are to be passed. In high voltage range, there is a gland plate which is to be drilled according to the size of the gland(s).
If the secondary of PT has reconnection, what shall I do with the other terminals?
Answer: It is only required to leave them open.
If we have taps in secondary of CT, what shall we do with the extra terminals?
Answer: It is enough to leave them open. (The main terminals shall be connected to the burden). In this rmanner, there is no risk.
If, by mistake, the secondary of a CT is open circuited, what shall I do?
Answer: In first step, the transformer shall be deenergized and disconnected from the network. Then, megger test of 5 kV shall be performed on all secondaries. The results shall be compared with the initial values obtained in the commissioning tests. If a change of more than 20% is observed the transformers shall be sent to NTC for probable repair. In any case, it is better to send the transformer to NTC for this preliminary check too.
If, by mistake, the secondary of a PT is short circuited, what shall we do?
Answer: In a nurgent effort, the network shall be deenergized and the transformer shall be disconnected from it. Then, it shall be sent to NTC to check the internal insulation.
What are NTC Products in HV range?
Answer: Instrument transformers, condenser bushings and capacitors for more information click here.
What are the minimum cross section area and maximum length of cable(s) from instrument transformers to the control room?
Answer: These items are considered by the designer of measuring and control system. The burden resulting from the resistance of the cables shall be added to the sum of actual burdens of measuring /conrol equipment and ordered to NTC.
What are the products of Nirou Trans Company?
Answer: Please click here
What is the application of F-Terminal in HV current transformers and test tap in condenser bushings and why they shall be connected to earth when energized and not in use?
Answer: The signal on the terminal which is a sample of the high voltage has applications as follow:
– Check of being energized / deenergized
– Synchronization with the high voltage
– Supervision on the quality of internal insulation of the product
If while the ponduct is energized, the terminal is opened, probably too high voltage will appear on it which may be hazardeous to operators in addition to the damages to the main insulation or even explosion of the product.
– Check of being energized / deenergized
– Synchronization with the high voltage
– Supervision on the quality of internal insulation of the product
If while the ponduct is energized, the terminal is opened, probably too high voltage will appear on it which may be hazardeous to operators in addition to the damages to the main insulation or even explosion of the product.
What MV products are being produced in NTC?
Answer: Instrument Transformers, bushings
What range of specifications are covered by each of NTC products?
Answer: Please click here
What will happen if the secondary of a CT is open circuited?
Answer: Open circuit in secondary of CTs ressembles extremely high burden. So, it leads to voltage rise on open circuited terminals to dangerous levels which may threat safety and health of operators if in Open circuit in secondary of CTs ressembles extremely high burden. So, it leads to voltage rise on open circuited terminals to dangerous levels which may threat safety and health of operators if in touch with the transformer in addition to the damages in the internal insulation of the CT.
What will happen if the secondary of a CT is short circuited?
Answer: Nothing but the lack of expected current / signal in measuring/ protection circuit.
What will happen if the secondary terminals of PT are open circuite?
Answer: Nothing but the lack of signal/ current on measuring / protection device.
What will happen, if the secondary terminals of PT are short circuited?
Answer: Short circuit in secondary of PT resembles extremly high burden. So, it leads to very high currents in secondary which may result in burning of internal windings of the transformer. In this happening if the primary winding is burnt, the network will be earthed and there will be serious hazards such as fire and explosion.
Which standards govern design, production and test of NTC products?
Answer: IEC, BS, ANSI, special standards and specifications required by the customer.
Why there is no need to provide corona ring in NTC products?
Answer: Using the optimum design in our products has made the corona in normal use of the products so low that there is no need to add additional parts such as corona ring to comply with the requirements of electromagnetic comapatibility (EMC).