Why is copper preferred over aluminium for transformer windings?

Copper is much easier to work with in bending and reshaping.

It is more forgiving and reliable under electromechanical stress and vibration.

Copper is much easier to terminate reliably (clamping in terminals and joins, soldering) with much less fuss in preparation for high reliability joins.

Aluminium to copper junctions require special fitting to eliminate electrolysis.

 

First, aluminum's conductivity is lower than copper's. To compensate, aluminum wire must have larger cross-sections than the equivalent copper wire to offer the same conductance. This means windings wound with aluminum wire will likely have greater volume compared with an equivalent copper wire.

Copper displays low levels of creep. Under the extreme loading and temperature conditions of distribution transformer windings, creep rates of aluminium can be up to 25 times higher than for copper. This results in aluminium wound distribution transformers having a higher propensity to failure than copper wound ones.

Copper wires have no galvanic action, as they are the same element as the connectors, which are usually made of copper or brass (a copper alloy). Aluminium loses material through galvanic action, leading to a loss of contact. Copper is harder, stronger and more ductile than aluminium, expands less and does not flow at terminations. Consequently it does not require periodic inspection and tightening of screws. Aluminium flows away from the termination under pressure.

Copper wound distribution transformers are invariably smaller and lighter than aluminium wound ones of an equivalent capacity and energy performance. Since the resistivity of copper is 0.6 times that of aluminium, the cross-section of the aluminium conductor needs to be 1.66 times larger than that of the copper conductor for the same resistance. This results in a larger transformer core and volume, which also leads to a larger transformer tank than for the copper design. While aluminium is lighter than copper of an equal volume, in the case of distribution transformers, this advantage is nullified by the increased volume (and thus weight) of the conductor, steel core, tank and oil.

Finally, transformers with copper windings are often less expensive to manufacture than those with aluminium windings. This is because it is not just the cost of conductor, but also the cost of magnetic steel, tank and oil needed to achieve the specified energy performance level that determines the total transformer manufacturing cost

Technical Parameter for 6kV, 10kV& 30kVA-2500kVA With Off Circuit Dry Type Transformer

(KVA)Rated capacity	Voltage Combination			Connection Group Symbol	No-load Loss(W)	Load Loss (W)			No-load Current (%)	Short-circuit Impedance(%)
	High Voltage (KV)	Tapping ranges of High Voltage	Low Voltage(KV)			130℃(B) (100℃)	155℃(F) (120℃)	180℃(H) (145℃)
30	6 6.3 6.6 10 10.5 11	±2.5% ±5%	0.4	Dyn11 Yyn0	190	670	710	760	2	4
50					270	940	1000	1070	2
80					370	1290	1380	1480	1.5
100					400	1480	1570	1690	1.5
125					470	1740	1850	1980	1.3
160					540	2000	2130	2280	1.3
200		±2X2.5% ±5%			620	2370	2530	2710	1.1
250					720	2590	2760	2960	1.1
315					880	3270	3470	3730	1
400					980	3750	3990	4280	1
500					1150	4590	4880	5230	1
630					1340	5530	5880	6290	0.85
630					1300	5610	5960	6400	0.85	6
800					1520	6550	6960	7460	0.85
1000					1770	7650	8130	8760	0.85
1250					2090	9100	9690	10300	0.85
1600					2450	11000	11700	12500	0.85
2000					3050	13600	14400	15500	0.7
2500					3600	16100	17100	18400	0.7
1600					2450	1220	12900	13900	0.85	8
2000					3050	15000	15900	17100	0.7
2500					3600	17700	18800	20200	0.7

 

Technical Parameter for 20kV 50kVA-2500kVA With Off Circuit Dry Type Transformer

(KVA)Rated capacity	Voltage Combination			Connection Group Symbol	No-load Loss(W)	Load Loss (W)			No-load Current (%)	Short-circuit Impedance(%)
	High Voltage (KV)	Tapping ranges of High Voltage	Low Voltage(KV)			130℃(B) (100℃)	155℃(F) (120℃)	180℃(H) (145℃)
50	20 22 24	±2.5% ±5%	0.4	Dyn11 Yyn0	340	1160	1230	1310	2	5.0
100					540	1870	1990	2130	1.8
160					670	2350	2470	3460	1.8
200		±2X2.5% ±5%			730	2770	2940	3140	1.8
250					840	3220	3420	3660	1.8
315					970	3850	4080	4360	1.8
400					1150	4650	4840	5180	1.1
500					1350	5460	5790	6190	1.1
630					1530	6450	6840	7320	1
800					1750	7790	8260	8840	1
1000					2070	9220	9780	10400	0.85
1250					2380	10800	11500	12300	0.85
1600					2790	13000	13800	14800	0.85
2000					3240	15400	16300	17500	0.7	8.0
2500					3870	18200	19300	20700	0.7
2000					3240	16800	17800	19100	0.7
2500					3870	20000	21200	22700	0.7

 

Technical Parameter for 35kV 50kVA-2500kVA With Off Circuit Dry Type Transformer

(KVA)Rated capacity	Voltage Combination			Connection Group Symbol	No-load Loss(W)	Load Loss (W)			No-load Current (%)	Short-circuit Impedance(%)
	High Voltage (KV)	Tapping ranges of High Voltage	Low Voltage(KV)			130℃(B) (100℃)	155℃(F) (120℃)	180℃(H) (145℃)
50	35 36 37 38.5	±2.5% ±5%	0.4	Dyn11 Yyn0	450	1340	1420	1520	2.3	6
100					630	1970	2090	2230	2
160					0.79	2650	2810	3000	1.5
200		±2X2.5% ±5%			0.88	3130	3320	3550	1.5
250					0.99	3580	3800	4060	1.3
315					1170	4250	4510	4820	1.3
400					1370	5100	5410	5790	1.1
500					1520	6270	6650	7110	1.1
630					1860	7250	7690	8230	1
800					2160	8600	9120	9760	1
1000					2430	9860	10400	11100	0.75
1250					2830	12000	12700	13600	0.75
1600					3240	14600	15400	16500	0.75
2000					3820	17200	18200	19500	0.75
2500					4450	20600	21800	23300	0.75

 

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