✌🏿 🕣 👨🏼‍✈️ Features of power supply systems using DDIBP 👩🏿 👨🏽‍🎨 🎤

Butsev I.V.
drups2019@mail.ru

Features of power supply systems using Diesel Dynamic Uninterruptible Power Supplies (DDIBP)

In the following statement, the author will try to avoid marketing cliches and will rely solely on practical experience. HITEC Power Protection DDIBP will be described as test subjects.

DDIBP installation device

The DDIBP device, from the point of view of an electrician, looks quite simple and predictable.
The main source of energy is the Diesel Engine (DD), with sufficient power, taking into account the efficiency of the installation, for long-term continuous power supply of the load. This accordingly imposes rather stringent requirements on its reliability, readiness for launch and stability of work. Therefore, it is completely logical to use shipboard DDs, which the vendor repaints from yellow to his own color.

As a reversible converter of mechanical energy into electrical energy and vice versa, the unit includes a motor generator with a power exceeding the rated power of the unit to improve, first of all, the dynamic characteristics of the power source during transients.

Since the manufacturer claims uninterrupted power supply, there is an element in the installation that supports the load supply during transitions from one operating mode to another. An inertial storage device or induction clutch serves this purpose. It is a massive body that rotates at high speed and accumulates mechanical energy. The manufacturer describes his device as an induction motor inside an induction motor. Those. there are a stator, an external rotor and an internal rotor. Moreover, the external rotor is rigidly connected to the common shaft of the installation and rotates synchronously with the shaft of the motor generator. The internal rotor is additionally untwisted relative to the external and is actually a drive. To provide power and interaction between the individual parts, brush assemblies with slip rings are used.

To ensure the transfer of mechanical energy from the DD to the rest of the installation, an overrunning clutch is used.

The most important part of the installation is the automatic control system, which, analyzing the parameters of the individual parts, has an impact on the control of the installation as a whole.
Also, the most important element of the installation is a reactor, a three-phase inductor with a winding tap, designed to integrate the installation into the power supply system and allow relatively safe switching between modes, limiting equalizing currents.
And finally, auxiliary, but by no means secondary, subsystems - ventilation, fuel supply, cooling, and gas exhaust.

Operating modes of the DDIBP installation

I believe it would be useful to describe the various states of the DDIBP installation:

operating mode OFF

The mechanical part of the installation is not moving. Power is supplied to the control system, the DD preheating system, the floating charge system of the starter batteries, and the recirculation ventilation unit. After preheating, the unit is ready to start.

operation mode START

When the START command is issued, the DD starts up, which through the overrunning clutch spins the external rotor of the drive and the motor-generator. As the DD warms up, its cooling system is activated. After reaching the operating speed, the internal rotor of the drive begins to spin up (charge). The process of charging a drive is indirectly judged by the current it consumes. This process takes 5-7 minutes.

If there is external power, it takes some time for final synchronization with the external network and when a sufficient degree of common mode is achieved, the unit is connected to it.

DD reduces the speed and goes into a cooling cycle, which takes about 10 minutes, followed by a stop. The freewheel is disengaged and the further rotation of the installation is supported by the motor-generator with simultaneous compensation of losses in the drive. The installation is ready to power the load and goes into UPS mode.

In the absence of external power supply, the installation is ready to power the load and own needs from the motor generator and continues to work in the DIESEL mode.

operating mode DIESEL

In this mode, the energy source is DD. The motor-generator rotated by it feeds the load. The motor generator as a voltage source has a pronounced frequency response and has a noticeable inertia, with a delay in responding to sudden changes in the load. Because The manufacturer completes the installation with shipboard DDs. Operation in this mode is limited only by fuel reserves and the ability to maintain the thermal regime of the installation. In this operating mode, the sound pressure level near the unit exceeds 105 dBA.

UPS operation mode

In this mode, the power source is an external network. The motor generator connected through the reactor to both an external network and to the load operates in the synchronous compensator mode, within certain limits compensating for the reactive component of the load power. In general, the DDIBP installation, connected in series with an external network, by definition worsens its characteristics as a voltage source, increasing the equivalent internal impedance. In this operating mode, the sound pressure level near the unit is about 100 dBA.

In case of problems with the external network, the installation is disconnected from it, a command is issued to start the DD and the installation goes into DIESEL mode. It should be noted that the start-up of a constantly heated DD occurs without load until the DD shaft speed exceeds the remaining parts of the installation with the overrunning clutch closed. Typical start-up and exit times of the operating speed of the DD is 3-5 seconds.

operating mode BYPASS

If necessary, for example, during maintenance, the load can be transferred to the bypass line directly from the external network. Switching to the bypass line and vice versa occurs with an overlap in the response time of the switching devices, which avoids even short-term loss of load power since the control system seeks to maintain the phase-matching of the output voltage of the DDIBP installation and the external network. In this case, the operating mode of the installation itself does not change i.e. if DD worked, then it will continue to work or the installation itself was supplied from an external network, then it will continue.

operating mode STOP

When the STOP command is issued, the load power is switched to the bypass line, the power of the motor generator and drive is interrupted. The unit continues to rotate by inertia for some more time and after stopping, switches to the OFF mode.

Connection diagrams of DDIBP and their features

Single installation

This is the easiest way to use an independent DDIBP. The installation can have two outputs - NB (no break, uninterruptible power supply) without interruption of power supply and SB (short break, guaranteed power supply) with short-term power interruption. Each of the outputs can have its own bypass (see Fig. 1.).

Fig. 1

Critical load is usually connected to the NB output (IT, circulation pumps of the cold supply system, precision air conditioners), and the SB output is connected to the load for which a short-term power interruption is not critical (chillers of the cold supply system). In order to exclude the complete loss of power supply to the critical load, the unit output and bypass circuit are switched with time overlap, and the fault currents are reduced to safe values due to the complex resistance of a part of the reactor winding.

Particular attention should be paid to the power supply from the DDIBP non-linear load, i.e. load, which is characterized by the presence in the spectral composition of the current consumption of a noticeable number of harmonics. Due to the features of the synchronous generator and the connection circuit, this leads to a distortion of the voltage shape at the output of the unit, as well as the presence of harmonic components of the current consumption when the unit is powered from an external AC voltage network.

Below are images of the form (see Fig. 2) and a harmonic analysis of the output voltage (see Fig. 3) when powered by an external network. The harmonic distortion coefficient exceeded 10% with a modest nonlinear load in the form of a frequency converter. At the same time, the installation did not switch to diesel mode, which confirms that the control system does not monitor such an important parameter as the harmonic distortion coefficient of the output voltage. According to observations, the level of harmonic distortion does not depend on the power of the load, but on the ratio of the power of the nonlinear and linear load, and when tested for a pure active, thermal, load, the voltage form at the output of the unit is really close to sinusoidal. But this situation is very far from reality, especially with regard to the supply of engineering equipment,incorporating frequency converters, and IT loads, with switching power supplies, not always equipped with a power factor corrector (PFC).

Fig. 2 Fig.

3

In this and subsequent diagrams, three circumstances take on themselves:

Galvanic connection between the input and output of the installation.
The skew of the phase load from the output goes to the input.
The need for additional measures to reduce the harmonics of the load current.
The harmonic components of the load current and distortion caused by transients penetrate from the output to the input.

Parallel circuit

In order to power the power supply system, the DDIBP installations can be switched on in parallel, connecting the input and output circuits of individual installations. It should be understood that the installation loses its independence and becomes part of the system when the conditions of synchronism and phase matching are fulfilled, in physics this is denoted in one word - coherence. From a practical point of view, this means that all the installations included in the system should work in the same mode, i.e., for example, the option with partial operation from the DD, and partial from the external network is not valid. In this case, a bypass line is created common for the entire system (see Fig. 4).

With this connection scheme, there are two potentially dangerous modes:

Connecting the second and subsequent installations to the system output bus in compliance with coherence conditions.
Disconnecting a single installation from the output bus in compliance with coherence conditions until the output switches open.

Fig. 4

Emergency shutdown of a single installation can lead to a situation when it starts to slow down, and the output switching device has not yet opened. Moreover, in a short time, the phase difference between the installation and the rest of the system can reach alarm values, causing a short circuit mode.

Also pay attention to load balancing between the individual units. In the equipment considered here, balancing is carried out due to the falling load characteristics of the generator. Due to its non-ideal and non-identical characteristics of the instances of installations between installations, the distribution is also uneven. In addition, when approaching the maximum load values, distribution of such seemingly insignificant factors as the length of the connected lines, the points of connection to the distribution network of the plants and the load, as well as the quality (transition resistance) of the connections themselves begin to influence the distribution.

It should always be remembered that DDIBP and switching devices are electromechanical devices with a significant moment of inertia and tangible values of the time delay for reaction to control actions from the automatic control system.

Parallel circuit with medium voltage connection

In this case, the generator is connected to the reactor through a transformer with an appropriate transformation ratio. Thus, the reactor and switching machines operate at an “average” voltage level, and the generator operates at a level of 0.4 kV (see Fig. 5).

Fig. 5

With this use case, it is necessary to pay attention to the nature of the final load and its connection diagram. Those. if the final load is connected via step-down transformers, it must be borne in mind that connecting the transformer to the mains with a high degree of probability is accompanied by a core remagnetization process, which in turn causes an inrush of the current consumption and, consequently, a voltage drop (see Fig. 6).

Sensitive equipment in this situation may not work correctly.

At least the low-inertia light blinks, and the default frequency inverters of the electric motors restart.

Fig.6

Split Output Bus Circuit

In order to optimize the number of installations in the power supply system, the manufacturer proposes to use a circuit with a “split” output bus, in which the installations are parallel in both input and output, with each installation individually connected to more than one output bus. In this case, the number of bypass lines should be equal to the number of output buses (see Fig. 7).

It should be understood that the output buses are not independent and are galvanically connected to each other through the switching devices of each installation.

Thus, despite the manufacturer's assurances, this circuit is a single power supply with internal redundancy, in the case of a parallel circuit, having several outputs galvanically coupled to each other.

Fig. 7

Here, as in the previous case, it is necessary to pay attention not only to the load balancing between the units, but between the output buses.

Also, some customers strongly object to the supply of “dirty” food, i.e. the use of bypass, to the load in any operating modes. With this approach, for example, in data centers, a problem (overload) on one of the beams leads to a system crash with a complete disconnection of the payload.

Life cycle of DDIBP and its impact on the power supply system as a whole

Do not forget that the DDIBP installations are electromechanical devices that require careful, if not more, reverent attitude and periodic maintenance.

The service schedule includes decommissioning, shutdown, cleaning, lubrication (once every six months), as well as loading the generator to the test load (once a year). It usually takes two business days to service one installation. And the lack of a specially designed circuit for connecting the generator to the test load leads to the need to de-energize the payload.

As an example, we take an excess system of 15 parallel-working DDIBPs connected by the "average" voltage to the double "split" bus in the absence of a dedicated circuit for connecting the test load.

With such initial data, in order to maintain the system for 30 (!) Ty calendar days in a day mode, it will be necessary to disconnect one of the output buses to connect the test load. Thus, the availability of power supply for the payload of one of the output buses is 0.959, and in fact even 0.92.

In addition, a return to the regular payload power supply scheme will require the inclusion of the required number of step-down transformers, which, in turn, will cause multiple voltage dips in the entire (!) System associated with the magnetization reversal of the transformers.

Recommendations for the use of DDIBP

From the foregoing, a non-comforting conclusion suggests itself - at the output of the power supply system using the DDIBP, a high-quality (!) Uninterrupted voltage is present when all of the following conditions are met:

External power supply does not have significant shortcomings;
The system load is constant in time, active and linear in nature (the last two characteristics do not apply to data center equipment);
There are no distortions in the system caused by commutation of reactive elements.

Summarizing, we can formulate the following recommendations:

Separate the power supply systems of engineering and IT equipment, and divide the latter into subsystems, to minimize mutual influence.
Separate a separate network to provide the ability to service a single installation with the ability to connect an outdoor test load with a capacity equal to a single installation. Prepare a site and cable management for these purposes.
Constantly monitor the load balance between the busbars, individual units and phases.
, .
.
.
, .. (RSP), - .
.
, .
, .
Complete the installation with vibration sensors to prevent an emergency.
If sound and thermal fields change, vibration or extraneous odors occur, immediately decommission the units for further diagnosis.

PS The author will be grateful for the feedback on the subject of the article.

Publication on other resources and the media only with the written permission of the author.

Features of power supply systems using DDIBP