electrical engg

The basis of classifying whether a motor is HT (HV) or LT(LV) is based on the voltage level at which this motor is fed power.

The classification of voltage level as LV, MV, HV, EHV is defined by various standards. Please note that there are some differences between them eg as per IEC (being followed in in large numbe rof countries) 400V/415V/440V is termed as LV whereas in India 415V is termed as MV.

As far as issue for classifying the same rating of motor as LV or MV is concerend this happens in borderline cases. It depends upon the client and the consultant, also on the power system distribution design, whether to feed a particular rating say 200kW from 400V system or from MV system of 3.3kV or 5.5kV or 6.6kV. Acordingly the motor becomes LV or MV.

thank u for ur valuable clarification.

i am just confused, in electrical panel its written "DANGER HIGH VOLTAGE" whereas its only 220V,

shokran

rma

they have different voltage output. thats hteir difference.

Ht and lt can be the same power rate. no problem. but they are use differnt equipment which has different voltage rate.

and why these equipment have different voltage rate? you will be curious next step I think.

the simple answer is, they have different purposes.

Hi sabarinathsingh,

The basic concept is the higher the voltage the current is lower for the same wattage and the conductor size has to be large to carry higher current. With lower voltage the transmission loss and heating losses will also be high.When we design a motor with higher voltage the insulation level has to be more and the safety to operators to be ensured. More over the system voltage has to be changed if you use some particular motor with higher voltage. So all the parameters like size of motor and system voltage and safety of operation and financial implication are considered to arrive at a decision regarding voltage of motor for specific purpose.

Hai, The LT and HT ratings are classified mainly on the voltage ratings for the same capacity motors. The difference between them is voltage and also the type of Insulation used. As in the case of HT there more care has to be taken against High voltage and also against thermal overheat. Thanks, Vinod

Dear,

please may be noted that normally, to avoid large current in LT, HT (3.3KV to 11 KV normally) Motor are preferred. If you increase the voltage for the same KW, FLA (Full Load Ampere) will be much lesser, so its maintenance, as well operational aspects are much better. In the industries normally above 200 KW are using as 6.6 KV or above.

You can easily calculate the current for higher voltage rating at same KW / KVA / MVA (in case of Trafo).

Hope you will understand.

Regards,

J. P. Shukla

well,thank u.but in our case,there are 3 motors of 200 Kw.2 of them are H.T(6.6Kv) & 1 is L.T(415v).all are used for same purposes (in process point of view).so i am in doubt.when we use H.T the F.L.C will be less.so we can use all that 3 motors as H.T.but it is not so.why?

Hii,

Normally we consider LT(440V and below) and HT (Above 440V) in the case of motors. But some considers LV, MV and HV. But for some testing purposes its makes confusion(in my case Polarization index test - calls for HT motors). So my question is where this MV will fall into - LT or HT. Is there any standards mentioning that?

Thanks in advance