GRAMEYER GRTD-2000C15A Digital AVR - Digital Automatic Voltage Regulator for GRAMEYER Alternators | OEM Replacement

Short version. The GRTD-2000C15A is a Digital Automatic Voltage Regulator. It supplies the exciter field, senses the alternator output and corrects the difference several times a second. Its rating is 15 A class on the 2000 series, its field resistance window 6-50 ohm, its accuracy 0.5 per cent, and it is intended for machines whose field winding sits inside that window. Read the rest of this page as the detail behind those three figures.

Excitation architecture. Self-excited or PMG. That single sentence decides most of the regulator's behaviour in a fault: whether the field survives a close-up short circuit, whether the machine builds up from residual voltage on its own, and how much the terminal voltage dips when a large motor starts on the same bus. Never flash a field through the regulator. Disconnect the board, flash the field directly, then reconnect. Flashing through the AVR is how a working board becomes a failed board.

Sensing. Single-phase or three-phase RMS sensing. The sensing circuit is the regulator's only view of the outside world, so its wiring matters as much as its specification. A voltage error introduced by a loose terminal or a long run of untwisted cable is indistinguishable, from the regulator's point of view, from a genuine voltage error on the alternator. Where a spare is being held, hold the drawing with it. A board without its wiring diagram costs a shift of production time to install.

Power stage and field drive. Power input 170-300 Vac, 50 / 60 Hz, output Up to 126 Vdc. Field current rating 15 A class on the 2000 series, forcing capability Forcing limited, field resistance window 6-50 ohm. These are not independent numbers: the output voltage ceiling and the field resistance together set the maximum current the board can actually deliver, and the continuous rating is only reachable at the low end of the resistance window. A regulator rated for a minimum field resistance of a few ohms will not drive a high resistance field to full current, however good its specification looks on paper.

Accuracy and response. 0.5 per cent steady-state accuracy, Digital, configurable, thermal drift Low thermal drift. In practice the accuracy figure is the least interesting of the three. What an operator notices is recovery after a load step, which is governed by response and by available forcing current, and what a maintenance engineer notices after two years is drift, which is governed by the reference circuit and the ambient temperature inside the terminal box. If the machine will not hold voltage at all, disconnect the field and measure the sensing voltage first. That one reading separates a sensing fault from a field fault.

Frequency behaviour. Rated for 50 / 60 Hz, with Programmable volts-per-hertz curve. The frequency-sensitive function exists to protect the prime mover, not the alternator: as engine speed falls the regulator reduces excitation so the alternator stops demanding torque the engine cannot supply. Without it, an overloaded engine is dragged down until it stalls, and the alternator is blamed for a fault that belongs to the fuel or governor system. An alternator that has been rewound needs its field resistance re-measured, because a rewind commonly moves it by ten to twenty per cent in either direction.

Paralleling. Reactive droop, configurable. On a single set this circuit does nothing. On two or more sets it is the only thing that stops the machines from exchanging reactive power in a slow oscillation, and it is the first place to look when a parallel installation shows a circulating current that nobody can explain. A set that runs at reduced speed will show low voltage on any regulator. Check engine speed against the nameplate before touching the excitation system.

Protection built into the regulator. Over-excitation, loss of sensing, over-temperature. These functions protect the alternator and the regulator, not the installation. Downstream protection, loss of mains and reverse power all belong to the controller, and a site that relies on the AVR for them is a site that will eventually trip in a way nobody can explain. Never flash a field through the regulator. Disconnect the board, flash the field directly, then reconnect. Flashing through the AVR is how a working board becomes a failed board.

What it fits. Mid and large frame alternators. Lifecycle status: In production. Both halves of that sentence matter at order time. A board that fits perfectly but has been discontinued is a different commercial decision from one that fits and is in current production, and the price difference rarely reflects the difference in risk. A set that runs at reduced speed will show low voltage on any regulator. Check engine speed against the nameplate before touching the excitation system.

Field notes on this model. The GRTD range is Grameyer's digital line. The 2000 series variants, C15A, E15A, ES15A and ESCM15A, differ in the sensing arrangement, the communications option and whether the 15 A power stage is fitted, so the suffix has to be matched to both the alternator and the panel wiring. The 1100 is the smaller digital board for mid-size machines.

Where this regulator does not belong. A GRTD-2000C15A is a voltage regulator, not a protection relay and not a governor interface. If the site needs loss-of-mains detection, reverse power protection or synchronising, those functions live in the controller, not here. Expecting the AVR to carry them is how installations end up with a set that holds voltage beautifully and still trips the site on a mains failure.

Documentation that survives the job. Photograph the terminal block before disconnecting anything, and write the sensing tap and the field resistance on the inside of the terminal box lid. Ten years later that note is the only thing that will let the next engineer choose a replacement without a full survey.

Commissioning sequence. Start with the machine at rated speed, no load, and the field disconnected. Confirm the sensing voltage at the AVR terminals is inside the window the board expects, then connect the field with the voltage trim at minimum. Bring the trim up slowly and watch the field current, not the terminal voltage, because the terminal voltage will look correct long before the field current has stabilised on a cold winding.

The forcing margin. A regulator that can only just hold rated voltage at rated load has no forcing margin left, and the machine will dip on every load step. The GRTD-2000C15A is specified with a minimum field resistance of 6-50 ohm; staying comfortably above that minimum, rather than exactly at it, is what leaves the forcing margin that makes a set feel solid rather than merely adequate.

Voltage low under load only. This is the classic field current limit symptom. Measure the field current at full load and compare it with the 15 A class on the 2000 series figure for the GRTD-2000C15A. If the board is at its limit, either the board is too small for the alternator or the field resistance has risen. A rewind, a corroded terminal or a long cable run will all produce the same reading.

New, old stock or refurbished. Discontinued regulators are available as new old stock, which is genuine and works, and as refurbished, which is a gamble on how the board was stored. Ask which one is being quoted. A board that has spent ten years in a damp warehouse has aged electrolytics even though it has never been installed.

Where this regulator does not belong. A GRTD-2000C15A is a voltage regulator, not a protection relay and not a governor interface. If the site needs loss-of-mains detection, reverse power protection or synchronising, those functions live in the controller, not here. Expecting the AVR to carry them is how installations end up with a set that holds voltage beautifully and still trips the site on a mains failure.

Mounting orientation and cooling. Most AVR boards are convection cooled and assume the heatsink fins are vertical. Mounting a GRTD-2000C15A flat on its back inside a sealed box shortens its life even though the ambient temperature reads acceptable, because the local air around the thyristor is far hotter than the box average.