BTT-40B

BTT-40B current transformer unit in aircraft AC power systems

The BTT-40B is an aircraft current transformer unit used in AC electrical power systems of Soviet and Russian aircraft. It belongs to the protection circuit of the generator feeder, not to the power generation unit itself. In a typical installation, the unit monitors current in the AC feeder and gives a signal to the protection and control equipment when the line condition moves outside the allowed operating range. The BTT-40B is therefore checked together with the generator circuit, feeder wiring, differential protection equipment, and distribution panel components.

Differential protection signal from the BTT-40B unit

The unit converts primary feeder current into a rectified voltage signal used by aircraft protection circuits. This signal is not intended for cockpit indication by itself. It is sent to the related protection and control blocks, where it becomes part of the logic for detecting short circuits, overloads, or abnormal current distribution. In aircraft using a GT-40PCh-6 type generator, the BTT-40B works in the same protection chain as generator control equipment, contactors, feeder lines, and switching devices. If one part of this chain is replaced, the wiring and acceptance data should be checked rather than assuming that the transformer unit is the only fault source.

Aircraft application of BTT-40B

The BTT-40B is found on a wide range of aircraft and helicopters equipped with AC electrical networks of this class. Known applications include Tu-154, Il-62M, Il-76, Il-86, Yak-42, An-72, An-124 Ruslan, and Mi-8 helicopters in MT, MTV and AMT configurations, as well as Mi-26 helicopters. The installation point may differ by aircraft type. On transport aircraft it is usually tied into generator feeder protection and main AC distribution. On helicopters it is connected with the onboard AC generator system and the associated protection wiring. For ordering, the aircraft type alone is not enough. The unit should be matched against the electrical equipment list and wiring diagram.

Construction and service notes for BTT-40B

The BTT-40B is built as a compact transformer assembly with three single-phase transformer sections inside a cast aluminium housing. The internal components are compound-filled, which protects the assembly against vibration and moisture in normal aircraft service conditions. During maintenance, the block is normally inspected as part of the AC power generation and distribution system. Typical checks include wiring condition, connector integrity, signal output, and correct response of the protection circuit. The unit should not be treated as a simple passive coil when troubleshooting, because its output is used by other protection devices and depends on the complete circuit around it.

Identification and ordering of BTT-40B

Before ordering a replacement, the marking on the housing should be compared with the aircraft parts catalog, repair documents, or electrical system schematic. The abbreviation BTT can appear in other technical contexts, including ground equipment, but BTT-40B in this case refers to aircraft electrical equipment only. For mixed fleets and aircraft after overhaul, it is useful to provide a photo of the data plate and the generator feeder section from the documentation. The product is also known under alternative designations BTT-40B and БТТ-40Б.

Тип изделия: Авиационный блок трансформаторов тока
Функция: Формирование сигнала для дифференциальной токовой защиты генератора и фидера
Применение / Где используется: Системы электроснабжения воздушных судов
Система / Место установки: Цепь защиты генератора переменного тока / защита фидера генератора
Совместимые ВС / техника: Ил-18, Ил-62М, Ил-76, Ил-86, Ил-96-300, Ту-154, Ту-204, Як-42, Ан-22, Ан-74, Ан-124, Ми-8, Ми-8МТВ-1, Ми-171, Ми-26, Ми-28
Мощность генератора: 40 кВА
Номинальный первичный ток: 111 А при 208 В, 400 Гц
Выходное напряжение: 3.3–4.9 В, среднее значение выпрямленного напряжения
Габариты: 168 × 72 × 95 мм
Масса: Не более 0.85 кг
Документация: Этикетка изделия, приемочная документация и документация по системе электроснабжения ВС

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