or
½¼Iabc ½AIDABC½IABC (21:108)also
½¼IABC ½AIDabc½Iabc (21:109)where
½¼IADabc ½IADABC^1 (21:110)The closed delta connection can be difficult to apply. Note in both the voltage and current equations that
a change of the tap position in one regulator will affect voltages and currents in two phases. As a result,
increasing the tap in one regulator will affect the tap position of the second regulator. In most cases the
bandwidth setting for the closed delta connection will have to be wider than that for wye connected
regulators.
21.1.4.8 Open Delta Connection
Two single-phase regulators can be connected in the ‘‘open’’ delta connection. Shown in Fig. 21.20 is an
open delta connection where two single-phase regulators have been connected between phases AB and CB.
Two other open connections can also be made where the single-phase regulators are connected
between phases BC and AC and also between phases CA and BA.
The open delta connection is typically applied to three-wire delta feeders. Note that the potential
transformers monitor the line-to-line voltages and the current transformers monitor the line currents.
Once again, the basic voltage and current relations of the individual regulators are used to determine the
relationships between the source side and load side voltages and currents.
For all three open connections, the following general equations will apply:
½¼VLLABC ½aRVabc½VLLabc (21:111)½¼VLLabc ½aRVABC½VLLABC (21:112)ACIAIa
a
VCAVBCVabVcaVbc
IcbcIabIcbIbVABICBIB++++++−−−−−−
ssLSL
SLLFIGURE 21.20 Open delta type B regulator connection.