Phase Undervoltage (27P) Protection; Element Operation - Basler BE1-11g Instruction Manual

9424200994 Rev U 57

Phase Undervoltage (27P) Protection

Five phase undervoltage (27P) elements monitor the sensing voltage applied to the BE1-11g. An element
can be configured to protect against undervoltage when the phase voltage decreases below a defined
level.
The five, identical phase undervoltage protection elements are designated 27P-1, 27P-2, 27P-3, 27P-4,
and 27P-5. Element logic connections are made on the BESTlogic™Plus screen in BESTCOMSPlus® and
element operational settings are configured on the Undervoltage settings screen in BESTCOMSPlus. A
summary of the logic inputs and outputs and operational settings appears at the end of this chapter.
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Voltage, Undervoltage (27P)
HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), Voltage
Protection, Undervoltage 27P

Element Operation

Phase undervoltage protection can be used to prevent large transformer and equipment damage when an
undervoltage condition exists. For example, an undervoltage condition could occur when a tap changing
control fails.
Modes of Protection
Three modes of protection are available. The One of Three mode activates protection when one of the
three phases of voltage decreases below the Pickup setting. The Two of Three mode activates protection
when any two of the three phases of voltage decrease below the Pickup setting. The Three of Three
mode activates protection when all three phases of voltage decrease below the Pickup setting.
Voltage Response
The phase undervoltage element can be set to monitor VPP or VPN. This is determined by the 27/59
Mode parameter of the phase VT connections found on the System Parameters/Sensing Transformers
settings screen in BESTCOMSPlus. For more information on the VTP setup for PP or PN voltage
response, see the Configuration chapter.
Timings
The timing mode can be set for definite or inverse.
Inverse
When inverse timing is selected, a Curve setting is provided to select programmable or table curves. The
user can select integrating reset timing to make the protective element use integrated reset and emulate
an electromechanical induction disk reset characteristic. The undervoltage inverse time curve with default
constants is shown in the Time Curve Characteristics chapter.
Programmable Curves
The programmable curve can be used to create a custom curve by selecting constants in the inverse time
characteristic equation. When curve P is selected, the constants used in the equation are those defined
by the user. Characteristics for trip and reset programmable curves are defined by Equation 6 and
�������� ��������
Equation 7. Definitions for these equations are provided in Table 14.
���� = + �������� ���� =
| ���� − 1 |
���� − ����
���� ����
���� 2
Equation 6. Time Characteristics for Trip
Equation 7. Time Characteristics for Reset
BE1-11g Phase Undervoltage (27P) Protection