ABB SafeRing and SafePlus RMU (CCV, CCF, Air, AirPlus)

Short answer

SafeRing is ABB's ring main unit (RMU) for secondary distribution, and SafePlus is its modular, extensible version. The SF6 versions go up to 40.5 kV; SafeRing Air and SafePlus Air insulate with dry air up to 24 kV, and AirPlus uses a low global-warming-potential gas mixture for higher voltages. The designation (CCV, CCF...) tells you which functions the unit carries.

What it is and where it is used

The ABB SafeRing RMU is a compact ring main unit, and SafePlus is its modular, extensible version. Both combine, in one sealed tank, the functions to switch the underground distribution ring and protect the transformer, with fuses or with a vacuum circuit breaker and relay. They are built with SF6, with dry air (Air versions) or with the AirPlus mixture, depending on voltage and region.

They are installed in pad-mounted or indoor distribution substations, buildings, industry, and solar and wind farms. SafeRing and SafePlus switchgear remain under ABB Electrification. For the underlying principle see medium-voltage switch-disconnector and compact medium-voltage substation.

Variants: SafeRing CCV, CCF, SafePlus, SafeRing Air, AirPlus and SafeLink

Model	Application	Main difference
SafeRing CCF	Ring with one transformer	Two cable functions and one fuse function
SafeRing CCV	Ring with relay protection	Two cable functions and one vacuum breaker
SafeRing CCCF, CCCV…	More feeders	Combinations of three or more functions
SafePlus	Modular substations	Extensible, bolt-together modules
SafeRing Air / SafePlus Air	SF6-free up to 24 kV	Dry-air insulation
SafeRing AirPlus	SF6-free at higher voltages	Fluoroketone gas mixture
SafeRing / SafePlus in SF6	Up to 40.5 kV	Classic version
SafeLink	Compact ABB RMU	Its own range; data per its catalog

Main features

Sealed tank holding the busbars and switching devices; the gas or dry air is monitored with a pressure indicator. See SF6 density monitor.
Transformer protection with fuses (F) or with a vacuum breaker and relay (V); versions with a self-powered relay need no auxiliary supply. The choice and the relay are covered in fuse or breaker to protect an MV transformer and transformer-feeder relay; the tests before energizing are in RMU testing.
Earthing switch on every function, with interlocks.
Plug-in cable connections and voltage presence indicators.
Motor operation of the cable functions to automate the ring.

Communications and integration

Motorized SafeRing and SafePlus units are integrated into the utility SCADA with a remote-control unit that reports positions, fault passage and alarms over IEC 60870-5-104, DNP3 or IEC 61850. The V function is integrated through its relay, often from the Relion family. See ABB Relion 615 relay.

SafeRing and SafePlus catalog data

SF6 version. The SafeRing/SafePlus product catalog for 12 to 24 kV (1VDD006104, 2013 edition) states these ratings for the ring main unit:

Rating	12 kV	15 kV	17.5 kV	24 kV
Power-frequency withstand voltage	28 kV	38 kV	38 kV	50 kV
Lightning impulse withstand voltage	95 kV	95 kV	95 kV	125 kV
Short-time withstand current, 3 s	21 kA	21 kA	16 kA	16 kA
Short-circuit making current	52.5 kA	52.5 kA	40 kA	40 kA

The busbars and the cable switch-disconnector (C module) are rated 630 A. The fuse module (F) and the vacuum breaker module (V) are published at 200 A. For the C module, the catalog states a breaking capacity of 630 A for active load and closed-loop switching, 20 A for transformer no-load and 135 A for a single capacitor bank. The fuses follow DIN 43625, with a maximum size of 125 A at 12 kV and 63 A at 24 kV.

Tank and gas. It is a sealed 3 mm stainless steel tank, filled with SF6 at a rated pressure of 1.4 bar absolute at 20 °C. The manufacturer states an annual leakage rate below 0.1 %, an expected service life of 30 years and a tank pressure test at 2.64 bar absolute. A pressure relief is provided. The degree of protection of the live parts and the tank is IP67; that of the mechanism cover, IP2XC, and that of the cable covers, IP3X. A temperature-compensated pressure gauge can be supplied. The switch-disconnector is three-position, with a combined earthing function. The stated mechanical operations are 1,000 for the disconnector and for the earthing switch, 2,000 for the vacuum breaker of the V module and 30,000 for the breaker of the SafePlus CB module. The dimensions of a two-function unit are 1,336 mm high, 765 mm deep and 696 mm wide.

Transformer protection. For the V module, ABB recommends self-powered relays such as the REJ 603, and for versions with an auxiliary-powered relay it mentions the REF54x family. In every case, the relay of an installed unit should be checked against the nameplate and the dossier, because the families have changed since that edition.

SF6-free version. The SafeRing/SafePlus Air technical catalog, for 24 kV, publishes dry-air insulation with zero global warming potential, the same format and operation as the SF6 version, and a piston-type switch-disconnector for breaking in dry air. It states 630 A continuous, 20 kA short-time for 3 s, 50 kA peak, 50 kV power frequency, 125 kV impulse, and IAC A-FLR internal arc classification at 20 kA for 1 s. The tank is also sealed, with a service life above 30 years and leakage below 0.1 % per year, and the normal operating altitude goes up to 1,500 m, with a pressure adjustment above it. The C module is declared in class E3 and M1 for the switch-disconnector, and E2 and M0 for the earthing switch, and the catalog includes a DC cable test voltage of 60 kV for 60 minutes. Keep that value in mind when planning diagnostic cable tests on the feeders.

Internal arc. Because it is a self-contained system, the catalog states that an internal arc fault has no effect on the surroundings, and it describes an option with arc suppressors that limits the released energy and signals its operation with a contact. This behavior is taken into account when the unit goes in a small room or inside a compact substation.

Frequently asked technical questions

SafeRing documentation: ABB publishes catalogs and installation and operating instructions for each version; the unit’s dossier says which functions and options it has.
CCF or CCV for a transformer: fuses are common on small transformers; the breaker with relay, when selectivity or more functions are needed. The decision comes from the protection study.
Pressure indicator out of range: the unit must not be operated until it has been inspected.
SF6 regulations: ABB points to European Union restrictions on SF6 in medium voltage from 2026; elsewhere, check the local regulations before specifying.

How we help

We do not sell switchgear. At Tiza Group we test ring main units (insulation, contact resistance, mechanisms, interlocks and cables), review the transformer protection and support commissioning, in substations and in industry, in Colombia or elsewhere on request. See circuit breaker testing within testing and commissioning. Write to us through the contact page.

References

IEC 62271-200, metal-enclosed switchgear and controlgear for 1 kV to 52 kV.
IEC 62271-103, switches; IEC 62271-105, switch-fuse combinations.
ABB, SafeRing & SafePlus pages (global and UK), Secondary GIS page and news on SafeRing AirPlus.
Regulation (EU) 2024/573 on fluorinated greenhouse gases.

Frequently asked questions

What does SafeRing CCV or CCF mean?

The letters describe the unit's functions, from left to right. C is a cable switch-disconnector (ring in or out), F is a fused switch-disconnector combination that protects a transformer, and V is a vacuum circuit breaker with a protection relay. A SafeRing CCF has two cable functions and one fused transformer function; a CCV has two cable functions and one breaker function.

What is the difference between SafeRing and SafePlus?

SafeRing is the fixed-configuration RMU for secondary distribution networks. SafePlus is the modular version: it is built from modules and can be extended, so it is used when the substation needs more functions or room to grow. Both share ABB's gas or air insulation technology.

Is there a SafeRing without SF6?

Yes. ABB offers SafeRing Air and SafePlus Air, insulated with dry air, up to 24 kV, and the AirPlus line, with a fluoroketone-based gas mixture, for higher voltages. The SF6 versions cover up to 40.5 kV.