Hi @K4uLinalM ,
I've found only below infromation (hope it will be helpful):

System Event: SOGENOHV-    Negative variance General OH    
Debit Posting type: M137 - Negative Variance of General OH    
Credit Posting Type: M40 - Work in Progress

System Event: SOMTRLV+    Positive variance of direct material cost    
Debit Posting Type: M40 - Work in Progress    
Credit Posting Type: M120 - Positive Variance of Direct Material Cost

Best regards,
Adam

Hi, Lina, 
Both these postings are examples of variances of shop order costs.

These variances are differences between calculated and actual costs of shop order.  

Calculation of manufactured item cost is quite complex topic - too complex to discuss it on a forum like that. In principle, when shop order is created it has assigned BOM structure with estimated costs of materials and routing plan with estimated costs of machinery, and you are reporting actual consumption of time and materials - in case there are differences between calculations and actual report - variances are triggered.
 

You can review the business events mentioned above: