Desalter Power Faults

When significant differences occur among the three-phase currents of a desalter vessel, the cause is generally electrical in nature. Typical fault conditions include:

• Abnormal output of one phase of the transformer;
• Broken metal wires from the electrode plates, which are carried by the oil and float within the electric field zone;
• Deterioration of insulation of the electrode plate suspension system;
• Foreign objects attached to conductors, electrical components, or electrodes of one phase inside the desalter vessel;

An increase in electrostatic desalting current is a common operational issue. There are two main causes of this phenomenon: one related to changes in crude oil properties, and the other related to electrical equipment. Distinguishing between these two causes is the key to effective troubleshooting. When a current increase occurs, the first step is to observe whether the increase appears in a single phase or simultaneously in all three phases:

• If operating conditions have not changed and only one phase current increases, this indicates a problem with the electrical equipment or a specific electrode plate;
• In some cases, even when operating conditions remain unchanged, all three phase currents may increase simultaneously. This may be caused by changes in crude oil properties; however, there are also cases where operating conditions remain unchanged but all three phase currents increase with one phase rising more significantly, requiring careful judgment;
• If the current increase is due to higher crude oil conductivity, and one phase increases slightly more than the others, the issue can often be resolved by adjusting operating conditions;
• If all three phase currents increase and one phase rises exceptionally high or even causes a trip, there is likely a problem with the electrode or electrical equipment of that phase, and electrical components should be the primary focus of inspection;

Transformer tripping is mainly caused by enhanced electrical conductivity resulting from crude oil emulsification and high water content, which increases the current to a level that triggers a trip. The specific causes include:

• An excessively high oil–water interface level in the desalter vessel, resulting in water carryover with the crude oil;
• Excessive mixing intensity, leading to severe crude oil emulsification and water carryover;
• Heavy crude oil with poor oil–water separation characteristics, resulting in water carryover;
• A sudden increase in wash water injection rate, causing excessive water content and crude oil water carryover;
• Faults in the electrical equipment of the desalter vessel;

Corrective Measures:

• After a trip occurs, first check the interface level, current, temperature, and other key parameters to identify the cause, then take corresponding measures to restore power as quickly as possible;
• If the interface level is excessively high, first open the auxiliary water draw-off line to reduce the interface to a normal level. Afterward, re-energize the desalter vessel, then investigate and resolve the cause of the high interface;
• If the interface level is normal but the current was very high prior to tripping and the desalting temperature is relatively high, stop wash water injection, reduce the desalting temperature, and increase the demulsifier dosage; alternatively, reduce crude oil throughput to increase settling time and lower water content in emulsified oil, or reduce mixing intensity;
• If crude oil water carryover occurs or the wash water injection rate suddenly increases, stop water injection and increase water draw-off from the desalter vessel. Power can only be restored after the interface level is stabilized;
• If severe emulsification makes re-energizing difficult, reduce throughput and isolate the electrostatic desalter vessel. Allow the system to settle under static conditions, and only after closed-circuit energization is stable should the desalter be gradually brought back into service;
• If the issue is ultimately determined to be an internal electrical problem within the vessel, take appropriate actions based on its nature, such as power shutdown, water flushing, vessel steaming, or internal inspection;