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Hello all,
I am conducting an in-house test. Our device employs a linear transformer (insulation system: CLASS B) which has two output windings (one is 10V, the other is 18V). Each output lead has one fuse (external to the transformer, F2A for 10V and F3.15A for 18V). The primary winding has one built-in thermal cutout (125 degree). Two input fuses also can be considered as the protective devices for transformer (external to the transformer, T2A). According to the standard, it seems need to do the overload test as follows:
1) Overload the 10V secondary winding on the basis of F2A. The winding under test is loaded on 4.2A (2.1x 2A) and the other winding is loaded normally. The test duration is 30 min (fuse approved per IEC 60127). F2A shall be replaced by links of negligible impedance and all other protective devices shall be in place. If second protective device operates, the test is ended.
2) Overload the 18V secondary winding on the basis of F3.15A. The winding under test is loaded on 6.6A (2.1x 3.15A) and the other winding is loaded normally. The test duration is 30 min (60127 approved fuse). F3.15A shall be replaced by links of negligible impedance and all other protective devices shall be in place. If second protective device operates, the test is ended.
3) Overload the primary winding on the basis of T2A. The winding under test is loaded on 4.2A (2.1x 2A) which realized by loading the output winding. The test duration is 30 min (60127 approved fuse). T2A shall be replaced by links of negligible impedance and all other protective devices shall be in place. If second protective device operates, the test is ended.
4) Overload test based on the built-in thermal cutout. First step is to find out the maximum test current which can not cause the fuses and thermal cutout to operate. The test shall be last until thermal stability established.
It seems so complicated. Are the above mentioned methods correct? could I do the overload test only based on the built-in thermal cutout? I think that no winding temperature would exceed the 175 degree (limit for class B) since the built-in thermal cutout is 125 degree.
Thanks and regards.
I am conducting an in-house test. Our device employs a linear transformer (insulation system: CLASS B) which has two output windings (one is 10V, the other is 18V). Each output lead has one fuse (external to the transformer, F2A for 10V and F3.15A for 18V). The primary winding has one built-in thermal cutout (125 degree). Two input fuses also can be considered as the protective devices for transformer (external to the transformer, T2A). According to the standard, it seems need to do the overload test as follows:
1) Overload the 10V secondary winding on the basis of F2A. The winding under test is loaded on 4.2A (2.1x 2A) and the other winding is loaded normally. The test duration is 30 min (fuse approved per IEC 60127). F2A shall be replaced by links of negligible impedance and all other protective devices shall be in place. If second protective device operates, the test is ended.
2) Overload the 18V secondary winding on the basis of F3.15A. The winding under test is loaded on 6.6A (2.1x 3.15A) and the other winding is loaded normally. The test duration is 30 min (60127 approved fuse). F3.15A shall be replaced by links of negligible impedance and all other protective devices shall be in place. If second protective device operates, the test is ended.
3) Overload the primary winding on the basis of T2A. The winding under test is loaded on 4.2A (2.1x 2A) which realized by loading the output winding. The test duration is 30 min (60127 approved fuse). T2A shall be replaced by links of negligible impedance and all other protective devices shall be in place. If second protective device operates, the test is ended.
4) Overload test based on the built-in thermal cutout. First step is to find out the maximum test current which can not cause the fuses and thermal cutout to operate. The test shall be last until thermal stability established.
It seems so complicated. Are the above mentioned methods correct? could I do the overload test only based on the built-in thermal cutout? I think that no winding temperature would exceed the 175 degree (limit for class B) since the built-in thermal cutout is 125 degree.
Thanks and regards.