Protection for digital substations

Low-impedance ground faults are generally managed reliably with protection devices like the SIPROTEC 7SN60. The high sampling rate of SIPROTEC 5 devices allows for the integration of new, sensitive digital procedures for the reliable detection of high-impedance ground faults. The parts of the signal which are caused by the discharging and charging of the ground capacitances of the grid are of particular interest here. The active power in the zero-sequence system is a good criterion to detect the direction of the ground fault. As the charging takes place over a longer period of time with high-impedance ground faults, this part of the active power is available during this time period and can be integrated right from the ignition of the fault. This results in the active energy in the zero-sequence system. 

Radial systems do not pose a problem for determining the direction. In meshed systems, operational zero-sequence currents can falsify the resulting direction. These operational zero-sequence currents are eliminated by the new algorithm in order to determine the correct direction.

Arc fault protection is a relatively new technique employed for the fast clearance of arcing faults on busbars and within metal clad switchgear & associated cable boxes. The arc is detected using an optical sensor & the signal input to a protection device which also monitors the load current on the system. Conventional current based protection techniques are at times challenged by the nature of arcing faults, and can result in slow protection clearance times. Slow protection clearance times increase the risk to nearby personnel and increase the degree of damage to plant and equipment. By employing an optical detection technique, Arc Fault Protection results in fast clearance of arcing faults.

Phasor Measurement Units (PMUs) and its measured synchrophasors make a valuable contribution to the dynamic monitoring of transient processes in energy supply systems. Phasor Measurement Units (PMUs) measure current and voltage by amplitude and phase at selected stations of the transmission system. The high-precision time synchronization (via GPS) allows comparing measured values (synchrophasors) from different substations far apart and drawing conclusions as to the system state and dynamic events such as power swing conditions. 

All SIPROTEC 5 devices can be used as a Phasor Measurement Unit. When selecting the option “Phasor Measurement Unit”, the devices determine current and voltage phasors, provide them with highly accurate time stamps and transmit them for analysis together with other measured values (frequency, speed of frequency change) using the IEEE C37.118 communication protocol, which are typically sent to the control center.

SIGUARD PDP (Phasor Data Processor) is a system for Wide Area Monitoring and Grid Monitoring that, as its measured variables, uses synchrophasors from phasor measurement units serving as sensors. It helps with quick recognition of the current network situation and indicates both power swings and transient phenomena, transparently as well as instantly. Replication of the respective network topology is not required. The tool supports control center personnel in assessing critical grid situations and contributes to the taking of suitable action. As all measured results are stored, power system disturbances can be promptly analyzed.

DIGSI 5 is the versatile engineering tool for parameterization, commissioning and operating all SIPROTEC 5 devices. Its innovative user interface includes context-sensitive user instructions. Simple connection to the device via USB enables you to work with a device easily and efficiently. The full capabilities of DIGSI 5 are revealed when you connect it to a network of protection devices: Then you can work with all of the devices in a substation in one project.

DIGSI 5 offers superior usability and is optimized for your work processes. Only the information you actually need to carry out your tasks is shown. These can be reduced further using expanded filter mechanisms. The consistent use of sophisticated, uniform mechanisms in the user interfaces requires less training.