The NOJA Power RC control organizes overcurrent into three elements per direction (master, low set and high set), four setting groups and a reclosing function with a trip counter. This guide explains what each part does so the settings coordinate with the fuse and the rest of the network.
What is set in a NOJA control
This guide explains how the protection of a NOJA Power RC control (the cubicle of the OSM reclosers) is organized, so you understand what each setting decides. It is not a programming procedure: the figures come from each network’s coordination study. For the equipment and its control, see NOJA OSM and RC controls. On this point, read NOJA RC10 inputs, outputs and logic.
Three elements for each function
Phase current is monitored with overcurrent (OC), negative phase sequence (NPS) and earth fault (EF). Each has three elements per power-flow direction, forward or reverse:
| Element | Typical use | Curve |
|---|---|---|
| 1 (master) | Sets the maximum number of time-delayed trips in the sequence | Inverse or definite time |
| 2 (low set) | Fast trip to let the fuse operate, or a first stage | Inverse or definite time; allows maximum-current modification |
| 3 (high set) | Limits downstream exposure to high currents | Definite time only |
Each element can be directional. If it is not, it responds to forward and reverse flow alike. Inrush restraint does not apply to negative sequence.
Curves and modifiers
The control always carries the twelve ANSI curves, the IEC inverse definite minimum time curve and definite time. From the software, up to ten more curves can be added, taken from 43 non-standard curves or user-defined ones. Modifiers can be applied on top of the curve:
- Minimum definite time: stops an inverse curve from tripping before a given time.
- Maximum trip time: 120 s from the factory.
- Minimum current and maximum-current multiplier: trim the curve (the latter only on low-set elements).
- Additional time: adds a constant time.
- Fault reset time: how long the element must be out of pickup before the timer resets.
To understand the curve shapes, see IEC and IEEE inverse-time curves.
Reclosing and coordination
Automatic reclosing (79) runs the sequence of trips and closes defined by the reclose map. Each protection group has its own sequence counter. A global counter allows at most four protection trips regardless of source. The 79-3 and 79-2 options make lockout happen on the third or second trip.
To coordinate with other devices, the control offers:
- Zone sequence coordination (ZSC): if it detects that a downstream device has operated, it advances its counter one step, so fast times are kept for the first operations and slow times for the later ones.
- Sequence advance: advances the counter if it detects that the upstream device operated; it never causes a trip.
- Time to add (TTA): for series reclosers with the same curve; it requires voltage reclose control to be active.
- Maximum number of trips (MNT): limits low-set trips in a time window; 6 trips in 3 hours from the factory. When exceeded, fast trips are disabled.
If the unit is closed by a manual command or by a scheme such as automatic backfeed restoration, it stays in single-shot mode until the reclose time ends. If a fault occurs in that period, it locks out.
What to check before applying a setting
- The coordination study with the fuse or the head-end relay.
- That directional elements match the real flow direction.
- That the active group is the one that matches the state of the network.
- That the control has the firmware that supports the function: some functions depend on the version.
How we help
We prepare and load NOJA recloser settings remotely, from your coordination study or building it with you. See remote configuration for NOJA Power or, if the recloser trips on the network, the trip analysis.
Related guides
- NOJA OSM and RC-10, RC-15 and RC-20 controls
- NOJA CMS, DCM and WSOS5 software
- Automatic reclosing 79
- Phase and ground overcurrent protection
- Recloser
- NOJA RC10: Inputs, Outputs and Programmable Logic
References
- NOJA Power, RC control user manual, protection chapter (overcurrent, reclosing, ZSC, TTA, MNT).
- IEEE C37.2, device function numbers; IEEE C37.60 / IEC 62271-111.
Frequently asked questions
How many setting groups does the NOJA RC control have?
Four. Each group stores its own protection settings and can be activated according to the state of the network.
How many trips does reclosing allow before lockout?
Up to four protection trips. The control also offers the 79-3 and 79-2 options, which lock out on the third and second trip.
What is time-to-add (TTA)?
A function that adds a time margin to the instantaneous elements when two series reclosers share the same curve, so the upstream unit does not trip before the one nearest the fault.