Siemens 7UM85, 7UM62 and 7UM61 Generator Relays

Short answer

The Siemens SIPROTEC 7UM85 is the modular generator protective relay of the SIPROTEC 5 platform, for machines of any size and generator-transformer units. Its SIPROTEC 4 predecessors, the 7UM61 and 7UM62, remain widely installed in hydro, thermal and cogeneration plants; Siemens has withdrawn the 7UM61 from its catalog.

What it is and where it is used

The Siemens SIPROTEC 7UM85 is the generator protective relay of the SIPROTEC 5 platform. Siemens presents it as a modular device for generators of any size, in hydro plants, synchronous condensers and conventional plants, and for generator-transformer units, where it covers the machine and the unit transformer protection in a single device. Its predecessors, the SIPROTEC 4 7UM61 and 7UM62, remain in service in many hydro, thermal, cogeneration and industrial self-generation plants.

For an overview of generator functions, see synchronous generator and its protections and generator protection scheme.

Variants: 7UM85, 7UM62 and 7UM61

Model	Platform	Application and main difference
7UM85	SIPROTEC 5	Modular, for generators of any size and generator-transformer units
7UM62	SIPROTEC 4	Small, medium and large generators; differential for generator, motor or transformer
7UM61	SIPROTEC 4	Small and medium generators and motors; Siemens withdrew it from its SIPROTEC 4 catalog

For rotor earth fault protection, Siemens states that the 7UM62 and the 7UM85 need external coupling units (7XR family). When ordering or replacing a device, those accessories are reviewed too.

Main functions

Function	ANSI	What it provides for the generator
Generator or unit differential	87G, 87T	Internal fault in the stator or the transformer (guide)
Stator earth fault	59N, 64	Ground fault in the winding (guide)
Rotor earth fault	64R	First ground contact in the field circuit
Loss of excitation and underexcitation	40	Insufficient excitation (guide)
Overexcitation	24	High volts-per-hertz ratio (guide)
Reverse power	32	Motoring (guide)
Out-of-step	78	Pole slipping (guide)
Negative sequence	46	Unbalance that heats the rotor (guide)
Frequency	81	Operation outside the allowed range (guide)

Siemens also mentions shaft current protection and overexcitation with machine curves in the 7UM85. Which functions each device carries depends on the order code and the configuration.

The 7UM62 inside, according to its manual

The 7UM62 manual (edition 11.2017, firmware V4.70) is a useful reference because it details how each part of the machine is protected:

Inputs. Eight current inputs: three for each side of the protected object, plus two of them with sensitive transformers that measure secondary currents in the milliampere range. Four voltage inputs: three phase-to-ground and one displacement voltage input for stator and rotor earth faults.
Frequency. The relay continuously adapts its sampling frequency, and measurement accuracy holds between 11 Hz and 69 Hz, provided there is at least one AC quantity of 5% of the rated value. The manual also includes a start-up overcurrent stage for low speeds, for example when starting generators with a converter.
100% stator earth fault. It consists of two halves. The first is the 90% protection (displacement voltage at the neutral or at the grounding transformer, with optional directional earth current detection). The second is a third-harmonic protection. Together they cover the whole winding. As an alternative, the manual describes a 100% protection with a 20 Hz polarizing voltage. It is measured with the 7XT33 and 7XT34 devices and is sensitive even with large stator earth capacitances.
Rotor earth fault. There are two methods. The first uses symmetrical capacitive coupling of a system-frequency voltage into the excitation circuit. It takes the operating earth impedances and the brush resistances into account, and calculates the fault resistance with alarm and trip adjustable in ohms. The second is more sensitive: it injects a 1 to 3 Hz square-wave voltage with the 7XT71 device, with sensitivity up to 80 kΩ and an integrated test function. In both cases the external coupling device listed in the manual is needed.
Shaft current. An additional sensitive earth current function serves for shaft current monitoring and bearing fault detection, with high sensitivity through an FIR filter.
Inter-turn short circuit. It detects inter-turn faults in the generator by measuring the displacement voltage against the generator neutral.
Differential. It serves a generator, motor or transformer. It has a restraint characteristic and stability against unequal CT saturation. It blocks on second harmonic for inrush currents and on third or fifth harmonic for overexcitation. It includes built-in adjustment of the vector group and the transformation ratio.
Impedance and out-of-step. Two impedance zones plus an overreach zone switchable by binary input, and an out-of-step protection that distinguishes whether the swing center is in the grid or in the generator-transformer unit area.
Inadvertent energization. It quickly opens the generator breaker if the machine is energized while at standstill.
Motor protections. Starting, locked rotor, restart inhibit with calculation of the time until restart is allowed, and operation and starting statistics, so the same relay can protect a motor.
Utilities. Clock synchronizable by IRIG-B, DCF77, binary input or a command through the system port; commissioning aids such as connection checks and field rotation checks; up to four analog outputs depending on the variant; and supervision of 10 threshold values assignable with CFC.

One point of attention in these devices is the trip logic: a generator has breaker, field and turbine trips, and with so many functions the hard part is not setting any one of them but organizing what trips what.

Communications and integration

The 7UM85 uses the pluggable communication modules of SIPROTEC 5: IEC 61850, DNP3, IEC 60870-5-104 and Modbus TCP over Ethernet, IEC 60870-5-103 through serial modules, and PRP and HSR redundancy. It is configured with DIGSI 5.

The 7UM61 and 7UM62 have system ports with exchangeable modules: depending on the module, IEC 60870-5-103, PROFIBUS, DNP3, Modbus or IEC 61850. They are configured with DIGSI 4. See DIGSI software.

Frequently asked technical questions

7UM62 relay manual: the manual changes with the firmware version; one from another version may not match the settings in the device.
Loss-of-excitation trip when operating underexcited: the characteristic must respect the machine’s capability curve and the voltage regulator limiter.
Rotor earth fault that cannot be tested: it depends on the coupling unit and its connection; without it the function does not measure.
100% stator earth fault: it is achieved by combining functions (neutral voltage and third harmonic, or injection), and each has its own service condition.
Trip matrix: which function opens the breaker, the field or the turbine is where most field errors occur; it is reviewed against the plant’s philosophy.

If your device is no longer manufactured

Siemens withdrew the 7UM61 from its SIPROTEC 4 catalog, and the current generator line is SIPROTEC 5 with the 7UM85. Migrating is not copying settings: the functions, logic, inputs and outputs, coupling units and integration all change. We design the replacement, configure the new device and test it before the machine is synchronized again; see engineering design and studies.

How we help

At Tiza Group we configure and review generator SIPROTEC relays remotely, from the approved settings and the plant’s protection study, with a backup before and after each change. See remote configuration of Siemens SIPROTEC relays. If the machine tripped and the cause is unclear, send us the records for a trip analysis, or write to us through contact.

References

IEEE C37.2, standard for electrical power system device function numbers.
IEEE C37.102, guide for AC generator protection.
Siemens, profile and product page for the SIPROTEC 7UM85; manuals for the 7UM61 (V4.1) and 7UM62 (V4.7); SIPROTEC 4 catalog, edition 8.1.

Frequently asked questions

What is the difference between the 7UM61 and the 7UM62?

Both are SIPROTEC 4 generator protective relays. Siemens presents the 7UM61 for small and medium machines and the 7UM62 as the most complete device, for generators, motors and transformers, with differential. Together they covered everything from the smallest machines to the largest.

Where can I find the 7UM62 manual?

Siemens keeps the 7UM62 manual on its support portal by firmware version (for example, V4.7). The manual must match the version of the installed device; settings and files are handled with DIGSI 4.

Which Siemens relay replaces the 7UM62?

Siemens' current generator line is SIPROTEC 5, with the 7UM85. The change requires translating settings and logic, reviewing inputs and outputs, the coupling units for rotor earth fault and integration, and testing the new device with the machine.