A special form of transformer having one winding, a portion of which is common to both the primary and the secondary circuits. The current in the high-voltage circuit flows through the series and common winding (see illustration).

The current in the low-voltage circuit flows through the common winding and adds vectorially to the current in the high-voltage circuit to give the common winding current. Thus, an electrical connection exists between high-voltage and low-voltage winding. Because of this sharing of parts of the winding, an auto-transformer having the same kilovolt-ampere (kVA) output rating is generally smaller in weight and dimensions than a two-winding transformer. One possible disadvantage of auto-transformers is that the winding are not isolated from each other and that the auto-transformer provides no isolation of the primary and secondary circuits.

Construction

Core and coil assemblies are mounted on isolation pads to reduce noise.
Bolted coil terminations suitable for copper or aluminium cables.
Front & back covers are easily removable for service.
Up to IP42 steel enclosures are available with paint / powder coating having lifting and wheel arrangement. MS or Stainless Steel enclosures are optional.
CE Certified
Qualified to the seismic requirements
Copper (Cu) or Aluminium (Al) windings
Copper / Aluminium / GI grounding strap
Accessible mounting flanges with front/back slotted mounting holes make installation easier
100% Factory tested for shorts and coil integrity, current and loss, voltage, impedance and noise.
Clear, Comprehensive Documentation and labeling
With more severe requirements on test voltages and creep age distance and clearance in air because these transformers are often exposed to over voltage.
Input-side matching taps.
Connections to safe-to-touch screw / screw less terminals in accordance with IEC61558 / IEC60076
Additional clamp type terminal on request.
High-grade, vacuum impregnation in polyester impregnating resin.
Special versions available on request.

Applications

Auto transformers are used in applications where electrical isolation is not a critical requirement. When the ratio V2 : V1 is 0.3 or more they are used with advantage. The normal applications are motor starters & booster.

These are used in:

Voltage Stabilizers, Dimmers, Motor Starters, conversion between different system voltage like Indian to US of UK system voltages Etc.

Specification

Output VA range

0.5KVA to 5000KVA
Input voltage

Max. 750V
Output voltage

Max. 750V
Frequency

50 / 60 Hz
Vector group

Yn0
Protection index

IP00 max IP23 ( Other Available on special Request )
Insulation class

F / H
Ambient temperature

Max. 50 Degc
Efficiency

90 to 99 % ( over a range of capacity)
Reference Standards

IEC61558-2-2 /IEC60076 / IS2026 / IS11171

Always specify the Required KVA, highest voltage & lowest voltage rating in your order/ Requirement.

Design KVA	Length	Width	Height	X	Y	SLOT	Weight	Figure
0.5	180	125	200	160	90	8X20	11	A
0.75	240	121	240	160	75	8X20	13	A
1	240	120	240	160	75	8X20	14	A
1.25	240	135	240	160	90	8X20	19	A
1.5	240	145	240	160	100	8X20	21	A
2	300	150	300	180	90	10X25	26	A
2.5	300	160	300	180	100	10X25	30	A
3	300	170	300	180	110	10X25	34	A
4	300	180	300	180	120	10X25	41	A
5	360	200	360	200	135	13X28	53	A
6	360	210	360	200	145	13X28	61	A
7.5	360	210	360	200	145	13X28	65	A
10	360	215	360	200	150	13X28	72	A
12.5	360	215	360	200	150	13X28	83	A
16	420	250	420	220	170	13X28	110	A
20	420	260	420	220	180	13X28	127	A
25	480	285	460	220	200	13X28	161	A
30	520	315	520	220	200	13X28	201	A
35	520	315	520	220	205	13X28	222	A
40	550	320	550	220	210	13X28	232	A
45	550	350	550	220	210	13X28	261	A
50	550	400	550	220	265	13X28	260	A
60	600	400	600	400	270	17x35	285	B
75	600	500	600	400	265	17x35	329	B
100	600	500	600	400	270	17x35	400	B
125	750	450	700	400	240	17x35	500	B
150	750	450	700	400	240	17x35	550	B
200	1050	500	950	300-300	400	17x35	750	C
250	1200	500	950	350-350	400	17x35	825	C
300	1200	500	950	350-350	400	17x35	900	C
400	1250	600	1050	400-400	400	17x35	1200	C
500	1400	600	1050	400-400	500	17x35	1450	C

Note:

For higher rating contact us for more details. Dimension may change at the time of final design.

Figure For Type :- A

Figure For Type :- B

Figure For Type :- C

Motor Starting Applications

Three Phase Motor Starting Auto Transformers

PRIMA motor starting auto transformers have been an industry standard for many years. Auto transformers are a significant component of a motor controller. In its simplest form, motor starters start and stop a motor and protect against over voltage and under voltage. In most applications, a simple full-voltage magnetic starter places full voltage across the motor’s winding on startup and maintains full voltage at the motor during the run mode. For larger motors, or motors where the load is connected, the effect of motor-starting inrush can stress the electrical system with significantly lower currents in the distribution network. This can cause all manner of disruption to the system with subsequent interruption in the facility. In these cases, reduced-voltage starting must be applied. The addition of a motor starting auto transformer during the startup sequence limits the starting inrush current. The PRIMA 3P product line is designed for Medium Duty service including applications for drive loads such as pumps, compressors, conveners and fans.

PRIMA 3P Motor Starting Auto transformer: Three phase, 3 coil, suitable for motor starters with 3 contacts, connected in a three phase ‘Wye’ configuration. This provides balanced voltages across each phase.

Special Motor Starting Auto transformers. For applications requiring heavy duty service with frequent starts or jogging, high inertia loads such as paper or steel mill drives, medium voltage or other unusual demands,

PRIMA can offer specially designed units to meet your requirements. Please consult our sales offices.

Specification

Output VA range

5HP to 1000HP
Input voltage

Max. 750V
Output voltage

Max. 750V
Frequency

50 / 60 Hz
Vector group

Yn0
Protection index

IP00 max IP23 ( Other Available on special Request )
Insulation class

F / H
Ambient temperature

Max. 50 Degc
Starts per Hour

6 Starts ( Other available on request)
Time duration

15 Seconds (Other available on request)
Tapping

60% 70% 80% 100% (Special Configuration available on request )
Reference Standards

IEC61558-2-2 /IEC60076 / IS2026 / IS11171

HP	L	W	H	X	Y
10	205	150	240	165	75
15	205	160	240	165	92
20	205	165	240	165	102
25	310	170	245	255	92
30	315	170	245	255	92
35	310	175	240	255	105
40	310	185	240	255	105
45	310	200	245	255	120
55	310	220	255	255	135
60	310	230	285	255	130
90	365	240	385	300	140
100	365	240	385	300	160
150	365	240	385	300	165

HP	L	W	H	X	Y
10	205	150	240	165	75
15	205	160	240	165	92
20	205	165	240	165	102
25	310	170	245	255	92
30	315	170	245	255	92
35	310	175	240	255	105
40	310	185	240	255	105
45	310	200	245	255	120
55	310	220	255	255	135
60	310	230	285	255	130
90	365	240	385	300	140
100	365	240	385	300	160
150	365	240	385	300	165

HP	L	W	H	X	Y
10	205	150	240	165	75
15	205	160	240	165	92
20	205	165	240	165	102
25	310	170	245	255	92
30	315	170	245	255	92
35	310	175	240	255	105
40	310	185	240	255	105
45	310	200	245	255	120
55	310	220	255	255	135
60	310	230	285	255	130
90	365	240	385	300	140
100	365	240	385	300	160
150	365	240	385	300	165

Auto Transformer

Construction

Applications

These are used in:

Specification

0.5KVA to 5000KVA

Max. 750V

Max. 750V

50 / 60 Hz

Yn0

IP00 max IP23 ( Other Available on special Request )

F / H

Max. 50 Degc

90 to 99 % ( over a range of capacity)

IEC61558-2-2 /IEC60076 / IS2026 / IS11171

Always specify the Required KVA, highest voltage & lowest voltage rating in your order/ Requirement.

Figure For Type :- A

Figure For Type :- B

Figure For Type :- C

Motor Starting Applications

Three Phase Motor Starting Auto Transformers

Specification

5HP to 1000HP

Max. 750V

Max. 750V

50 / 60 Hz

Yn0

IP00 max IP23 ( Other Available on special Request )

F / H

Max. 50 Degc

6 Starts ( Other available on request)

15 Seconds (Other available on request)

60% 70% 80% 100% (Special Configuration available on request )

IEC61558-2-2 /IEC60076 / IS2026 / IS11171

Our Clients

HP	L	W	H	X	Y
10	205	150	240	165	75
15	205	160	240	165	92
20	205	165	240	165	102
25	310	170	245	255	92
30	315	170	245	255	92
35	310	175	240	255	105
40	310	185	240	255	105
45	310	200	245	255	120
55	310	220	255	255	135
60	310	230	285	255	130
90	365	240	385	300	140
100	365	240	385	300	160
150	365	240	385	300	165