field test

CIRCUIT DIAGRAM FOR FIELD’S TEST

EM1 LAB,BCVR,RAJAHMUNDRY Prepared by K. Nagesh & V.D.Neelima

Drop Test for RAG Generator:

Drop Test cicuit (RAM )Motor

Drop Test cicuit (RSEM ) Motor

Drop Test cicuit (RSEG ) Generator


FIELDS TEST ON DC SERIES MACHINE

AIM: To conduct Field’s Test of two similar machines and draw efficiency curves.

APPARATUS:

S.No Name of the Equipment Range Type Qty.

1 Ammeter 0 – 20A M.C 1No2 Ammeter 0 – 10A M.C 1No.3 Voltmeter 0 -300V M.C 3Nos

4 Rheostat 13.6 Ω/20A Wire wound 1No.

5 Tachometer 0- 10,000rpm Digital 1No.

THEORY:-

This test is applicable to two similar series motors. Series motors which are mainly used for traction work are easily available impairs In this method two identical coupled machines mechanically and electrically coupled are required. This test gives efficiency of both machines, “M” acting as motor drives machine”G” as a generator. The series field of both M & G are connected in series with motor armature in order that the load is not thrown off accidentally the generator armature is connected to load directly with out any switch.. One machine runs normally as a motor and drives generator whose output is wasted in a variable load resistance. Iron and friction losses of two machines are made equal (i) by joining the series field winding of the generator in the motor armature circuit so that both machines are equally excited and (ii) by running them at equal speed

PROCEDURE:-

1. Connect the circuit as shown in figure.

2. By closing the DPST switch apply 220V D.C Supply

3. Adjust the motor rheostat such that motor attains rated speed.

4. Vary the load resistance and note down voltmeter or ammeter reading.

5. Load resistance is varied until the motor current reaches its full load.

TABULAR FORM :

S.NO Vt Vm Vg Im Ig Wcm Wo Wcg Wc Motor efficiency

Generator efficiency


Drop Test for Ra ( Motor& generator ) :

S.No. Voltage ( V ) Current in ( A ) Armature Resistance Ra = V / I

1234

Tabulation for Rse ( motor &generator )

S.No. Voltage ( V ) Current in ( A ) Armature Resistance Rse = V / I

1234

Model Graph :

Model Calcualations:-

Vt = ______ IM =________ VM =________VG =________ IG =_______

RaG =______ RseG =______ RseM =_______RaM =_______

Total Input = VM IM =__________ W

Total Output = VG IG = __________ W

Losses of two machines = I/P - O/P = __________ W

WC = __________ W


WC = (Total losses – Im2 RSEM – IM

2 RAM – I2G RSEG - I2

G RAG ) 2

Motor Input = VM IM =________

Motor losses = WC + IM2 RseM + IM

2RaM =________W

Motor Output = Input - losses =_________W

ηM = O/p x 100 =________ I / P

Generator output = Vg Ig = _________W

Generator losses = WC + Ig2 Rag + Ig2Rseg =________ W

Generator Input = output + losses = __________W

ηg = output x 100 = __________ Input

Precautions:-

1. The motor should must be started with any load.2. Motor rheostat should be kept in maximum resistance position.3. Both motor and generator should be coupled before starting the system.4. Readings should be taken with out parallax error.

RESULT:-

The field test on two similar machines is conducted and also efficiency curves are drawn for both generator & motor.

VIVA VOCE1. What is the application of series motor2. Why the motor should started on load3. Which efficiency is greater when compared to motor and generator


field test

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