Beatrice Lang
Elevators are powered by a combination of mechanical and electrical systems, with electricity powering the motor that moves the car up and down the shaft. The electrical design of an elevator is regulated by various codes and guidelines, which can be intimidating to designers and engineers. The power for the elevator controller must enter a lockable safety disconnect device, and a separate insulated grounding conductor is required to run from the electrical source to the elevator controller. Elevators are equipped with safety mechanisms to ensure passenger well-being during power outages, such as backup power systems that maintain essential systems like intercoms, alarm bells, lighting, and fans. These backup systems can include generators, batteries, and uninterruptible power supplies (UPS).
| Characteristics | Values |
|---|---|
| Electricity in elevators | Converts electric energy into mechanical energy to move elevator cabs up and down |
| Power source | Electricity powers the motor, which moves the car up and down the shaft |
| Power backup | Most modern elevators have a small backup power source to maintain essential systems such as intercoms, alarm bells, lighting, and fans inside the cab |
| Power outage safety mechanisms | Elevators are equipped with safety mechanisms to ensure passenger well-being during power outages. In the event of a power outage, the elevator's momentum might carry it to the nearest floor, where passengers can exit |
| Power outage communication systems | Communication systems allow passengers to communicate with building management or emergency services and call for help |
| Power outage lighting | Backup lighting provides visibility inside the elevator car during a power outage |
| Power requirements | The power for the elevator controller must enter a lockable safety disconnect device, which must be either a fused disconnect or a circuit breaker |
| Power regulations | Various codes and guidelines regulate the electrical design of elevators, and designers must understand these basics to handle the pressure |
| Power and fire safety | Smoke detectors are required in all elevator lobbies and equipment rooms and must be connected to the elevator controllers directly or indirectly through output signals from the fire alarm control panel |
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What You'll Learn
Backup power systems
Elevators are required to have backup power systems to ensure the safety of passengers and the functionality of critical systems in the event of a power outage. The type of backup power system depends on the elevator's design and local regulations.
One common backup power system is the Uninterrupted Power Supply (UPS), a battery-powered system that kicks in immediately during a power failure. UPS systems are popular due to their lower upfront costs and ability to work with standard elevators and elevators with regenerative power. However, they may not provide sufficient power for long-term operation. Regulations require UPS systems to support the elevator and its accessories for at least 90 minutes under maximum load conditions.
Another backup power option is a generator, which provides limited power to elevators during outages. In the case of power surges, generators can protect elevators from potential damage. Regulations require that the generator activates within 60 seconds to power at least one elevator in the building.
To ensure the safe evacuation of passengers, some elevators are equipped with a battery-lowering system or automatic rescue device. When normal power is disconnected, this system activates and safely lowers the elevator to a nearby level, opening the doors for passengers to exit.
Additionally, emergency lighting is a crucial aspect of elevator backup power requirements. Elevator cab lights must be connected to an emergency power supply, either from the building's emergency power or a battery backup unit provided by the elevator supplier. This lighting ensures a safe path of egress during power outages.
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Electrical safety
Elevators are a very safe mode of transportation, with over 325 million daily riders on some 700,000 elevators in the US. However, electrical safety is paramount, and there are many codes and guidelines that regulate the electrical design of elevators.
Smoke Detectors and Fire Safety
Smoke detectors are required in all elevator lobbies and equipment rooms. They are connected to the elevator controllers, and in the event of a fire, the elevator is directed to travel to a designated landing, open its doors, and remain stopped until the alarm clears. This designated landing is usually at grade level for quick passenger exit.
Power and Emergency Backup
The power for the elevator controller must pass through a lockable safety disconnect device, which can be a fused disconnect or a circuit breaker. A separate circuit is required for cab lighting and accessories, and it too must have its own disconnect and overcurrent protection device (OCPD). Elevator cab lights are also required to have emergency backup power to ensure lighting in the event of a power outage.
Maintenance and Servicing
During maintenance and servicing, electrical safety devices play a crucial role. They monitor the position of mechanical locking devices, ensuring that elevator movement is prevented when necessary. These safety devices also ensure that any working platforms are fully retracted and that stop doors are mechanically locked.
Passenger Safety
Passengers can also take certain precautions to ensure their safety when using elevators. It is important to stand clear of the doors, allow exiting passengers to leave first, and wait for the next car if the current one is full. In the event of a fire or power disruption, it is advised to take the stairs. If an elevator becomes stuck between floors, it is safest to remain inside and use the intercom to call for assistance.
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Smoke detectors
When a smoke detector is activated, it triggers the elevator's "Fire Recall Function." This function is designed to bring the elevator cab to a designated landing, typically the floor on the grade level, where passengers can quickly exit to safety. The elevator doors will open, and the cab will remain stationary until the alarm is cleared. This pre-programmed response ensures that individuals can evacuate the building efficiently during a fire.
The placement of smoke detectors is also important. While only one smoke detector is required at each floor lobby, it must be located within 21 feet of every elevator door. This proximity ensures that the detector can effectively sense smoke and activate the necessary safety protocols. In large equipment rooms, a horn/strobe alarm may be installed to ensure that any alarms are audible despite the noise and isolation of these spaces.
To further protect passengers and equipment, safety protocols dictate that the power source to the elevator control panel should shut down before the discharge of water from a sprinkler head. This measure helps prevent electrical hazards during fire suppression. Depending on local codes, heat or smoke detectors may be installed within 24 inches of sprinkler heads to facilitate this. In the case of hydraulic elevators, a safety feature called a "rescuvator" can be specified to prevent occupants from becoming trapped due to power loss when a heat detector is activated.
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Power conversion
Single-phase power is often associated with slower and less efficient elevator operation. In contrast, three-phase power is the preferred option for commercial elevators, offering improved performance. When considering power conversion for elevators, it is essential to identify the specific voltage and phase balance requirements of the elevator system. Some elevators have strict voltage balancing modulation systems, requiring a tight voltage balance between phases.
To address the challenges of power conversion, various solutions are available, including phase converters. Phase converters provide an economical and reliable alternative to the costly installation of three-phase power. NAPCco, for instance, offers single-to-three-phase motor converters, which are particularly useful for elevators with multiple power requirements. Digital rotary phase converters are a popular choice, as they utilise microprocessors and solid-state relays to control three-phase power effectively. These converters ensure balanced power distribution and sufficient voltage to meet motor starting requirements, making them a continuous and economical power solution.
Analog rotary phase converters are another option, producing a true analog sine wave similar to that of a power station. These converters can achieve high efficiency ratings of up to 98% and offer a simple user interface. Additionally, AC to DC power conversion is also mentioned as a potential solution for elevators, fire pumps, and other applications.
Elevator systems are also becoming more energy-efficient. Manufacturers are employing strategies such as counterweights to reduce the required motor output. Regenerative drives further contribute to energy conservation by converting wasted energy during descent into electricity that can be fed back into the building's electric grid for reuse. These advancements not only improve energy efficiency but also help optimise the performance of elevator systems. Overall, power conversion techniques are vital in ensuring elevators meet their power requirements while also adhering to economic and efficiency constraints.
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Electric motors
There are two main types of electric motors used in elevators: DC motors and AC motors. DC motors are conceptually simple and capable of quality operation, but they are more mechanically complicated and require increased maintenance, making them more expensive to run. DC motors can rotate because the electricity fed into the rotor windings is commutated or switched. The polarity of the electrical supply can be switched to reverse the direction of rotation, which is useful for elevators. However, this feature is not available in single-phase AC motors as the polarity is constantly switched. Brushless DC motors are a variation that eliminates the disadvantages of standard DC motors, such as dust and heat generation, and radio frequency interference.
AC motors, on the other hand, are externally commutated, with the switching already built into the electrical supply. They can be either synchronous or asynchronous (induction). The AC power from the supply is fed directly into the stator windings, creating a rotating magnetic field. AC motors with a capacity of more than 5 hp, which is typically required for elevators, use three-phase power. This involves three separate circuits with wires in common, 120° out of phase, supplying power to the motor housing.
The speed of an AC motor is frequency-dependent, and it can be slowed by reducing the voltage to induce stalling. However, this is not an efficient way to control speed. Some AC motors have two speeds, achieved through separate windings and separate wires for each speed. Permanent-magnet gearless motors are a more recent innovation in elevator technology. They are smaller than traditional designs but offer comparable power.
To ensure the safe operation of electric motors in elevators, regular maintenance is necessary. This includes checking the connections for corrosion, damage, or looseness and replacing any faulty components. Additionally, the insulation on the power wire should be inspected, and grease should be applied to grease fittings as needed.
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Frequently asked questions
During a power outage, elevators stop working as they rely on electricity to operate. Most modern elevators are equipped with backup power systems, such as generators, batteries, and uninterruptible power supplies (UPS), to maintain essential systems such as intercoms, alarm bells, lighting, and fans.
Smoke detectors are required in all elevator lobbies and elevator equipment rooms. When a smoke detector goes off, it signals the elevator to go into "Fire Recall Function". The elevator then travels to its pre-programmed designated landing, opens its doors, and remains stopped there until the alarm clears.
Regenerative drives in elevators convert excess energy produced during descent into reusable electricity, which can be fed back into the building's electric grid for reuse.
There are numerous codes and guidelines that regulate the electrical design of elevators. Power for the elevator controller must enter a lockable safety disconnect device, which can be a fused disconnect or a circuit breaker. A separate insulated grounding conductor must be run from the electrical source to the elevator controller. Additionally, elevator cab lights require emergency backup power to ensure visibility during power outages.
