Voltage Regulator Controls: TAPCON, SEL-2414, M-2001D, CL-7

Short answer

A transformer voltage regulator (function 90) decides when the tap changer goes up or down to hold the bus voltage. The most commonly installed are the Maschinenfabrik Reinhausen TAPCON, the SEL-2414, the Beckwith M-2001D and, in line regulators, the Eaton CL-7 with the VR-32 regulator. This sheet summarizes what each one does and how it integrates with SCADA.

What it is and where it is used

A transformer voltage regulator, function 90 in ANSI numbering, compares the measured voltage with the setpoint and commands the on-load tap changer to raise or lower a tap, with a time delay that avoids unnecessary operations. On distribution networks the same name is used for the line voltage regulator, an autotransformer with a step tap changer installed on the circuit. The function, independent of any brand, is explained in automatic voltage regulator 90.

The most commonly installed controls are the TAPCON from Maschinenfabrik Reinhausen (MR), the SEL-2414, the Beckwith M-2001D and, in line regulators, the Eaton CL-7, which controls regulators such as the VR-32 from the former Cooper. Siemens JFR step regulators are also found on distribution networks.

Variants: TAPCON, SEL-2414, M-2001D, CL-7 and VR-32

Model	Application	Main difference
TAPCON 230 (BASIC, PRO, EXPERT)	Transformer with on-load tap changer	MR’s current generation; dynamic setpoint TDSC, line-drop compensation; paralleling in PRO and EXPERT
TAPCON 250	Transformer, North American market	MR’s standard control for North America; DNP3 and IEC 61850, web HMI, adapter panels for retrofit
TAPCON 260 and earlier	Transformer	Earlier MR generations still in service
SEL-2414	Transformer	Tap changer control plus thermal monitoring, cooling, loss of life and through-faults
Beckwith M-2001D (M-2001C, M-2001B)	Transformer and substation and line regulators	Adapter panels, R-X or Z compensation, VAr bias, paralleling
Eaton CL-7 (CL-6)	Line voltage regulators	SCADA-ready control, compatible with most regulators in service
VR-32	Single-phase line regulator	Autotransformer with a 32-step tap changer, ±10 %

Main functions

Function	ANSI	What it adds
Voltage regulation with bandwidth and delay	90	Keeps the bus or load-point voltage within the band
Line-drop compensation (LDC)	90	Regulates voltage at a remote point of the network, not only at the bus
Transformer paralleling	90	Avoids circulating current between transformers in parallel
Overcurrent and undervoltage blocking	—	Prevents tap changes during faults or without a reference voltage
Reverse power flow detection	—	Adjusts regulation when power reverses, for example with distributed generation

To go deeper into the blocking functions, see undervoltage protection 27.

Communications and integration

SEL-2414: IEC 61850 Edition 2, DNP3, Modbus, PRP, PTP and SNTP, plus SEL’s own protocols (Mirrored Bits, Fast Meter).
Beckwith M-2001D: Modbus, DNP3 and IEC 61850, over copper or fiber Ethernet and serial ports.
TAPCON: connection to SCADA; the TAPCON 250 lists DNP3 and IEC 61850.
Eaton CL-7: SCADA-ready, with a single communication point.

Configuration is done with each manufacturer’s software (AcSELerator QuickSet for the SEL-2414, for example). See IEC 61850 digital substation.

How a tap changer control regulates: what is not always explained

Basic regulation compares the measured voltage with a setpoint and a band. Modern controls add functions that change the behavior of the network and that are worth understanding before deciding what to enable. According to the SEL-2414 datasheet (in English), the device offers:

Configurable band and delays: the band center is set in secondary voltage and the width in percent. The delay for the first tap can be inverse, linear or hyperbolic, so that a large deviation acts sooner than a small one.
Forward and reverse power flow: locked-forward, locked-reverse, bidirectional and cogeneration modes. With distributed generation on the feeder, flow can reverse, and a regulator designed only for forward flow stops regulating well.
Line-drop compensation (LDC): compensates the resistive and reactive drops between the transformer and the regulation point, with different values for forward and reverse flow.
Voltage reduction: up to three levels for short-term demand, activated from SCADA or from local logic.
Runback on high or low voltage: brings the voltage back to the band without waiting for the normal delay.
Up to 32 tap positions and 3 neutrals, read by a 4–20 mA, ±1 mA or 0–2 mA transducer, or by a BCD or binary indicator, with operation counters per position and a record of up to 100 tap change events.

Besides the control, the SEL-2414 watches the transformer. It calculates the hot-spot temperature with IEEE C57.91-2011 or IEC 60076-7:2018 edition 2, and monitors up to ten RTDs (resistance temperature detectors) or thermocouples. It also alternates and exercises the cooling fan banks, and records the through-fault currents that wear the transformer. That information is the basis of a maintenance plan for the tap changer and the transformer; see online transformer monitoring.

Transformers in parallel: methods and their conditions

Two or more transformers with tap changers feeding the same bus must be regulated in a coordinated way. If each one regulates on its own, circulating current appears between them. The German manufacturer A. Eberle describes these paralleling methods, which also appear, under other names, in the controls of other brands and in the IEEE C57.153 guide:

Method	How it works	Condition or limit
Master-slave	One regulator commands the tap and the others repeat it	Requires communication between controls and identical transformers; an initial tap difference is kept, not corrected
Master-follower	Each follower reads the master’s tap and moves to the same position	Corrects the initial difference; admits different rated powers if the same tap gives the same ratio, and relative short-circuit voltages that differ by no more than 10 %
Circulating reactive current (ΔI·sinφ)	Each control calculates the circulating current by subtracting the load part and shares it equally	Needs to exchange values over the network of controls
Power-weighted ΔI·sinφ	Same, but the sharing is proportional to rated power	Needs the rated power of each unit
Δcosφ	Each control compares its reactive current with what it would have at a setpoint power factor	No link between controls needed; works in meshed networks and as an emergency backup

Source: A. Eberle documentation (English). Some practical points that follow from it:

With different no-load voltages between transformers, reactive circulating current appears because the impedances are low.
A tap change on one unit only partly moves the bus voltage; with n identical units the effect is roughly 1/n.
If the taps do not match, the bus voltage can be correct and current still circulates.
If the link between controls fails, the circulating-current methods switch to Δcosφ with the last measured power factor and return to the original method when communication is restored.

The SEL-2414 allows up to four transformers to operate in parallel, with two independent groups, through preconfigured Ethernet communication between the controls. The MR TAPCON 230 offers paralleling in its PRO and EXPERT versions, according to Reinhausen; the BASIC version does not include it. More detail on the principle is in paralleling transformers with tap changers.

Bay controllers with built-in regulation

Some bay controllers include the voltage regulation function, such as the GE C264 with its AVR (automatic voltage regulator). According to the manufacturer’s brochure, it regulates one to four transformers in parallel, with active and reactive compensation to regulate at a remote point, circulating current minimization and master-follower mode. See MiCOM C264 bay controller. The advantage of that architecture is one device less in the panel; the cost is that a change in the bay logic can affect the regulation, which is why tests are done together.

Frequently asked technical questions

M-2001B and M-2001C controls versus the M-2001D: the M-2001D is the current version of the line; replacement is done with adapter panels the size of the original control.
CL-7 control manual: Eaton publishes the CL-7 control manual; the regulator’s manual (VR-32 or another) is separate.
The regulator changes taps too many times: usually a band that is too narrow, a short delay or a poorly set line compensation.
Transformers in parallel with circulating current: the paralleling method and the signals between controls are not well configured.

How we help

We do not sell regulators. At Tiza Group we configure tap changer controls and voltage regulators of any brand, remotely worldwide or on site in Colombia, or elsewhere on request: setpoints, compensation, paralleling, blocking and their integration into SCADA. See remote relay configuration and, for integration over IEC 61850 or DNP3, control, protection and communications configuration. On site we test the tap changer and the transformer in testing and commissioning. Write to us through contact.

References

IEEE C37.2, function numbers (90); IEEE C57.91 and IEC 60076-7, loading of transformers; IEC 60214-1.
Maschinenfabrik Reinhausen, TAPCON 230 and TAPCON 250 pages; SEL, SEL-2414 page; Hubbell Beckwith Electric, M-2001D; Eaton, CL-7 control and VR-32 regulator.

Frequently asked questions

What is the SEL-2414?

It is a SEL device that combines on-load tap changer control and transformer thermal monitoring. It regulates voltage with forward and reverse power flow, coordinates up to four controls in parallel over Ethernet, controls cooling from the hot-spot temperature, calculates loss of life according to IEEE C57.91 or IEC 60076-7 and records through-faults. It communicates over IEC 61850 Edition 2, DNP3 and Modbus.

What is the Beckwith M-2001D used for?

It is a digital tap changer control from Beckwith Electric, now part of Hubbell, for transformers with an on-load tap changer and for substation and line regulators. It installs with adapter panels the size of the original control, has line-drop compensation, transformer paralleling and communication over Modbus, DNP3 and IEC 61850. It is the current version of the M-2001 line, which includes the M-2001C and M-2001B.

What is the CL-7 control of a Cooper voltage regulator?

It is the voltage regulator control from Eaton, which bought Cooper Power Systems. Eaton presents it as SCADA-ready and able to operate almost any voltage regulator in service, such as the VR-32 single-phase step regulator. It replaces earlier generations such as the CL-6.