Power Factor and Dissipation Factor Testing Methods:Basic Test Connections (Test Modes) for PF Testing

Basic Test Connections (Test Modes) for PF Testing

To help understand the PF test operation, it is convenient to consider the relative connections of the AC source, the bridge circuit, and the test specimen with respect to ground and the LV lead(s). Figure 3.5a through c shows basic test configurations that simplify testing on complicated insulation systems inside HV apparatus.

Grounded-Specimen Test Mode

In grounded-specimen test (GST) mode, all current between the AC source and ground (through CX) is measured by the bridge (Figure 3.5a). GST is used when one terminal of the insulation to be measured is permanently connected to ground, such as a bushing flange, transformer tank, or grounded apparatus frame. GST mode also connects the LV lead(s) directly to ground. This enables the lead(s) to be used to ground a specimen terminal that is not normally grounded.

GST Mode with Guard (GST-G)

In Doble test sets this connection is referred to as guard-specimen test mode. In this mode, all current between the AC source and ground (through CX)

is measured by the bridge (Figure 3.5b). The LV lead(s) may be connected to the test circuit guard. Any current present on the LV lead(s) during the test are bypassed directly to the AC source return, and are eliminated from the measurement. GST-G mode is used to isolate an individual section of insula- tion and test it without measuring other connected insulation.

Ungrounded-Specimen Test Mode

In ungrounded-specimen test (UST) Mode, only current between the AC source and the LV lead (through CX)is measured (Figure 3.5c). Any current flowing to a grounded terminal is bypassed directly to the AC source return, and is eliminated from the measurement. UST mode is only used to measure insulation between two ungrounded terminals of the apparatus. In UST mode, ground is considered guard since grounded terminals are not mea- sured. UST mode is used to isolate an individual section of insulation and test it without measuring other connected insulation.

Incoming search terms:

• grounded specimen test
• UST mode
• ungrounded specimen test
• Ungrounded Speciman Test
• gst electrical testing
• testing ust gst gst-g
• ust ungrounded specimen test vs gar
• Basic Test Connections (Test Modes) for PF Testing Grounded-Specimen Test Mode Grounded-Specimen Test Mode GST Mode with Guard (GST-G) Ungrounded-Specimen Test Mode
• gst vs ust mode tan delta testing
• what is grounded specimen test