NOJA Power

Technical Article

Updated 12/2021

Protection Feature Application Summary

Modern digital protection relays offer extensive functionality, and NOJA Power’s RC series controllers are no exception. While the vast majority of users will only apply Overcurrent, Earth Fault and Sensitive Earth Fault (Ground fault to our US users) features to protect their distribution networks, we often receive questions regarding the applications for the many other features on offer. This exploration of features can highlight the shortcomings of existing protection schemes which may be addressed by enabling existing features within the controller.

Our protection feature summary diagram has become one of the most accessed images in our documentation. While it summarizes the NOJA Power RC’s capabilities, it only enumerates the features. The application of these features is assumed knowledge.

To address this knowledge assumption gap, below is a table of all the protection functions in NOJA Power’s RC Control System, and their key applications. That is, why these features are used in practice.

Feature NameANSI CodeApplications
Overcurrent50P, 51PDetecting Overloads, currents exceeding equipment ratings
Earth Fault50G, 51GDetecting a failure of insulation in a circuit, causing a connection to earth. Reduced efficacy in non-effectively earthed networks
Sensitive Earth Fault50SG, 51SGDetects High Impedance earth faults and insulation failure
Negative Sequence Current50Q, 51QDetect Current Imbalance, such as broken conductors or wiring errors.
Broken Conductor46BCExploits the ratio between Positive Sequence and Negative Sequence current, allowing detection of broken conductors without needing units of impedance
High Z Fault DetectionNot ANSI DefinedDetects Very High Impedance earth faults and earth faults on resonant/isolated neutral networks
Neutral Admittance21YNDetects earth faults on isolated neutral networks.
Fault Locator21FLProvides location estimates of overcurrent faults in distance from OSM Recloser
Harmonic RelayNot ANSI DefinedDetects failing inverter equipment and industrial/generation connections violating connection code
Directional Overcurrent67PProvides selectivity of overcurrent protection in scenarios of varied load flow
Directional Earth Fault/SEF67G, 67SGProvides selectivity against sympathetic capacitive earth fault currents in high capacitance networks.
Directional Power32Provides anti-motoring and anti-generating features for distribution network connected rotating machines.
Reclosing79Provides Automatic Circuit Reclosing to improve network reliability. Ensures quantity of fault current applied to clear faults remains within equipment nameplate constraints. Exploits fault statistics that indicate 80% of faults are momentary and do not necessitate outages.
Circuit Breaker Failure50BFProvides a breaker state logical output for substation interlock schemes. Used for inter-trip schemes on critical protection path
Under Voltage27Protects against brownout conditions, and can be used to prevent back-feed of power in distributed automation schemes. Can also be used for load shedding
Over Voltage59PProtects against equipment damage from voltage exceeding nameplate ratings
Vector Shift78VSApplied for non-synchronous generation connection and anti-islanding.
Neutral Overvoltage59NUsed for Earth Fault detection on isolated neutrals. Generally applied in conjunction with current elements such as SEF
Over Frequency81OUsed to detect excess generation
Under Frequency81UUsed to detect generation shortfalls and islanding
ROCOF81RAddresses the non-detection zone of OF and UF by acting on the rate of change of frequency. Used for distributed generation connection and anti-islanding protection
Sync Check25Interlock feature mandating synchronism of load and source side before a close command can be issued
Auto-Synchroniser25AAn automation of Sync Check. Initiation of a close command starts a timer, and a close will occur when synchronization criteria are satisfied. If the timer expires, the close command is discarded

All these protection features are available in NOJA Power’s RC-10, RC-15 and RC-20 controllers.

“Modern reclosers offer far more than the original ball and chain solutions developed in the 1930s and we are proud to be leading the way in terms of functionality available today,” reports NOJA Power Group Managing Director Neil O’Sullivan.
1930’s era Recloser with Ball and Chain Hydraulic Mechanism
1930’s era Recloser with Ball and Chain Hydraulic Mechanism

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