L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
2-1
L30 Line Current Differential System
Chapter 2: Product description
Product description
This chapter outlines the product, order codes, and specifications.
2.1 Product description
The L30 Line Current Differential System is part of the Universal Relay (UR) series of products. It is a digital current
differential relay system with an integral communications channel interface.
The L30 is intended to provide complete protection for transmission lines of any voltage level. Both three phase and single
phase tripping schemes are available. Models of the L30 are available for application on both two and three terminal lines.
The L30 uses per phase differential at 64 kbps transmitting two phaselets per cycle. The current differential scheme is
based on innovative patented techniques developed by GE. The L30 algorithms are based on the Fourier transform–
phaselet approach and an adaptive statistical restraint. The restraint is similar to a traditional percentage differential
scheme, but is adaptive based on relay measurements. When used with a 64 kbps channel, the innovative phaselets
approach yields an operating time of 1.0 to 1.5 cycles (typical). The adaptive statistical restraint approach provides both
more sensitive and more accurate fault sensing. This allows the L30 to detect relatively higher impedance single line to
ground faults that existing systems may not. The basic current differential element operates on current input only. Long
lines with significant capacitance can benefit from charging current compensation if terminal voltage measurements are
applied to the relay. The voltage input is also used for some protection and monitoring features, such as directional
elements, fault locator, metering, and distance backup.
The L30 is designed to operate over different communications links with various degrees of noise encountered in power
systems and communications environments. Since correct operation of the relay is completely dependent on data
received from the remote end, special attention must be paid to information validation. The L30 incorporates a high
degree of security by using a 32-bit CRC (cyclic redundancy code) inter-relay communications packet.
Several options are available for communication. An RS232 port (USB port with the graphical front panel) can be used to
connect to a computer for the programming of settings and the monitoring of actual values. The rear RS485 port allows
independent access by operating and engineering staff. It can be connected to system computers with baud rates up to
115.2 kbps. All serial ports use the Modbus RTU protocol. The IEC 60870-5-103 protocol is supported on the RS485
interface. IEC 60870-5-103, DNP, and Modbus cannot be enabled simultaneously on this interface. Also only one of the
DNP, IEC 60870-5-103, and IEC 60870-5-104 protocols can be enabled at any time on the relay. When the IEC 60870-5-103
protocol is chosen, the RS485 port has a fixed even parity and the baud rate can be either 9.6 kbps or 19.2 kbps. The
100Base-FX or 100Base-T Ethernet interface provides fast, reliable communications in noisy environments. The Ethernet
port supports IEC 61850, IEC 61850-90-5, Modbus/TCP, TFTP, and PTP (according to IEEE Std. 1588-2008 or IEC 61588), and
it allows access to the relay via any standard web browser (L30 web pages). The IEC 60870-5-104 protocol is supported on
the Ethernet port. The Ethernet port also supports the Parallel Redundancy Protocol (PRP) of IEC 62439-3 (clause 4, 2012)
when purchased as an option.
